Categories
WW2 American Prototypes

Heavy Tank T29

USA (1944-48)
Heavy Tank – 10 Built

The U.S. Army did not prioritize addressing the need for heavily armored tanks until very late in World War II, when the losses of Allied armor were increasing due to enemy anti–tank guns. The M4A3E2, a makeshift assault tank developed from the M4A3 Sherman, was only produced as a stopgap measure until the T26E3 Pershing was available for reinforcement. Unfortunately, these heavy tanks were still not considered enough.

The T29 was developed to solve this problem. Armed with a long-barreled 105 mm T5E1 gun in a heavily armored turret, and weighing over 66 tons (60 tonnes), it was intended to directly engage with any opposition, from fortified bunkers to heavily armored tanks. Over a thousand were planned for production, with the first tank being completed in July 1945, too late to see action against Germany in Europe. The production would continue for a planned invasion of Japan, Operation Downfall, until its cancellation after the nuclear bombing of Hiroshima and Nagasaki, followed by the surrender of Japan, ending the war in Pacific.

Even after WWII, experiences gained from the war were carried over to the T29 and the design underwent numerous experiments for postwar development studies, which led to the production of the 120mm Gun Tank M103.

T29 heavy tank at the Aberdeen Proving Ground on 31 October 1947. Source: Firepower

Prelude

The development of a new heavy tank was first requested by the Chief of Research and Engineering of the Ordnance Department, General Gladeon M. Barnes, on 1 August 1944. He called General John B. Waldron, the Assistant Deputy Commissary of the Ordnance, about an Ordnance Committee Minute for a new heavy tank project. Gen. Waldron told Gen. Barnes that the project must be considered before such a vehicle could be passed for production. The inspection of the tank details took place at the Detroit Arsenal on the following day by the Ordnance Board and the Armored Center. It was expected that the new vehicle would be armed with a 105 mm cannon.

On 14 September 1944, OCM 25117C specified that, in order for a tank of greater firepower to be developed to meet potential operational requirements against fortifications and heavily armored enemy combat vehicles, it was considered imperative that the development of such a vehicle should be initiated immediately. Preliminary studies had been made for the installation of a 105 mm cannon in a tank with cross-drive transmission, torsion bar suspension and center-guided tracks, all powered by a 750 hp Ford petrol engine.

These studies had indicated the feasibility of this project. It was recommended:

  • That four pilot vehicles in general accordance with the characteristics outlined in this item be procured for test. Two to be fitted with 105 mm gun and two with 155 mm gun.
  • That the vehicles with the 105 mm gun be designated as Heavy Tank, T29.
  • That the vehicles with the 155 mm gun be designated as Heavy Tank, T30.
  • That these projects be considered confidential.
Schematics of T29 Heavy Tank. Source: AFV Technical Situation Report No. 33

Development

The first concept of the Heavy Tank T29 was initiated on 1 August 1944 with a proposal of what was essentially an enlarged T26 heavy tank sporting a 105 mm cannon. The initial specification was laid out with OCM 25117, suggesting a heavy tank weighing 54 tonnes and having an effective frontal armor thickness of 8.9 inches (228 mm), with a front hull armor of 5 inches (127 mm) angled at 46°. It also had a large mantlet covering the entire front turret, with 7.9 inches (203 mm) of armor backed with an internal armored plate. The turret design was to be made as simple as possible, with a 4 inch (102 mm) thick turret wall with nearly vertical inclination and streamlined. It was to have a stepped turret roof identical to that of the T26 turret, although it was noted to be a flaw in the protection due to the potential threat of deflecting projectiles. A large bulge was to be constructed at the rear of the turret to balance the turret assembly and the gun mount likewise.

The original concept of the Heavy Tank T29. Source: Development History of the Heavy Tanks, T29 & T30

The crew arrangement placed the commander on the right side of the turret, provided with a vision cupola. The gunner was in front of him, with the loader on the left side of the turret, provided with a single escape hatch. The driver and the co–driver were in the front hull. The armament consisted of a 105 mm T5 L/48 gun (a derivation of the prototype 105 mm T4 anti-aircraft gun intended for tank use), using stub fixed-type ammunition with just a single loader. A muzzle velocity of 2799 fps (853 m/s) for the armor-piercing round was expected. The main armament would have an elevation ranging from –10° to +20° and a .30 caliber (7.62 mm) Browning M1919A4 machine gun would be mounted coaxially. An anti-aircraft .50 caliber (12.7 mm) Browning M2HB heavy machine gun was also placed on top of the turret to be used by the loader. The tank would be powered by a Ford V12 petrol engine and a new cross–drive transmission developed by General Motors. The suspension used a similar approach to that of the T26, with torsion bars and center guided tracks.

However, the initial specification was revised a month later in favor of increasing firepower and a design overhaul. The front hull armor was switched to 4 inches (102 mm) angled at 54°, while maintaining the same effective armor thickness as previously. The general design of the turret received minor changes. The front plate of the turret remained the same but the rear bulge was increased in depth and reduced in thickness to 3 inches (76 mm). The 105 mm T5 L/48 gun was replaced with a much longer 105 mm T5E1 L/65, using large separated type ammunition. The turret now accommodated two loaders for the new shell loading type. The muzzle velocity was increased to 2,998 fps (914 m/s). A muzzle brake was developed for the new gun as a blast deflector, designed as an enlarged version of the 90 mm gun muzzle brake.

Contracts were awarded to the Pressed Steel Car Company for the construction of the tank and to Buick for the transmission development. The first pilot turret was to be mounted on the M6A2E1 in order to conduct trials in place of the T29. The second pilot turret assembly was being produced in February 1945 and expected to arrive in June. At the same time, a further design had been prepared and a new wooden mockup was built. The design received major alterations, with the turret wall now curved throughout the side to reduce the height of the turret. The roof plate was crested in the center to clear the gun breech and sloped down to either side of the turret walls to prevent shot deflection inside the turret. The actual weight of the turret was unchanged, and any weight savings were used to increase the armor protection. The thickness had been increased; 5.9 inches (158 mm) from the front to sides, tapering to 5 inches (127 mm) on the centerline of the turret, and 102 mm to the rear. The rear bulge of the turret was thickened again to 102 mm. The turret body was cast with the roof and the floor welded in position.

Wooden mockup of the second turret. Source: AFV Technical Situation Report No. 34

The gun mount was redesigned with the 105 mm T5E1 repositioned so that it would balance on its trunnions without the need for an equilibrator (although the installation of a muzzle brake would negate this). The recoil distance of the 105 mm gun was limited to 12 inches (305 mm) and regulated by three hydraulic cylinders located above the barrel. A recoil guard was fitted to the gun mount and extended from the gun cradle to the breech face. The single coaxial M1919A4 was replaced with two M2HB for increased firepower.

The main sight for the gunner was an M10E5 periscope with dual sights, 1x for a wide field of view, and 6x for high magnification, fitted with a reticle graduated for the 105 mm T5E1. An auxiliary telescope M70E2, a special M70 direct telescope lengthened by 15.7 inches (40 cm), occupied the vision port on the right side of the 105 mm gun with 3x magnification. An azimuth indicator was located on the gunner’s right. Elevation was controlled by means of a vertical handwheel and traverse by powered hydraulic control. An emergency hand traverse crank was also available. The gun traverse was equipped with a 5 hp power unit to drive the pump. The turret could be satisfactorily traversed either manually or by power traverse on a 30° slope. The power traverse system was designed to allow turret rotation at a speed of 3 rpm (18°/second). A full 360° turret rotation took 20 seconds. A gun traverse lock was located under the traverse pump and in front of the gunner, which consisted of a toothed segment that could be clamped into the traverse rack.

The primary firing controls consisted of an index finger trigger on the handle of the power traverse gear operating the main gun. A thumb button was provided to fire the coaxial machine guns. Secondary foot firing gear was also arranged beside the main one.

Separate ammunition was issued for the 105 mm T5E1. The shells would be derived from the ones for the 105 mm T4 gun, with the T12 HE and T13 APCBC–HE, weighing 38 pounds (17.2 kg) and 41 pounds (18.6 kg) respectively, with 33 pounds (15 kg) of propellant charge. 63 complete rounds were stowed and 46 of the projectiles were packed in bins inside the racks on either side of the commander. It was intended that the commander should pass these projectiles to the loaders. Nine charges were stowed in ready racks, 7 for the left loader and 2 for the right loader. The remaining ammunition was stored in the hull. Additional stowage for 23 boxes (110 rounds each) of .50 cal machine gun rounds was provided.

The commander’s seat in the turret bulge with the cupola above. Source: AFV Technical Situation Report No. 34.

The turret crew was reshuffled to adapt with the second turret. The commander sat right behind the 105 mm gun, and the cupola was moved to the center rear of the turret. There were now two loaders stationed on both sides of the turret, provided with their respective escape hatches. The right loader had access to a pistol port to his side, and the left loader could use the .50 caliber machine gun mounted outside the tank. The gunner retained his original seat at the front right side of the turret, though now distanced away from the commander.

The gunner’s fire control, including telescopic and periscopic sights inside the second wooden turret mockup. Source: AFV Technical Situation Report No. 34.

Two pilot tanks were being constructed by the Pressed Steel Car Company in March 1945. The T29 was planned for production with as many as 1,200 units, with 2 pilots to become available earlier for preliminary testing. Chevrolet worked on the turret and gun mount. Frankford Arsenal was given a directive for designing and manufacturing the fire control installations. The development of the engine and transmission would be undertaken by the Detroit Transmission Division of General Motors, whilst Buick inspected the final drive. Work on the T5E1 was temporarily suspended pending details of the new rounds and chamber design. In the redesign, provision for the subsequent scavenging device installation was being made.

The pilot turret received some modifications during production. The elevating gear was now anchored to the turret ring, whilst the box which contained the nut and screw elevation gear was mounted on the gun cradle. The main ventilation for the crew consisted of a 28.3 m3/min fan set to draw air from an inlet between the driver and co–driver. In addition, there was a blower fan with an inlet on the right side of the turret bulge, close to the deflector guard, intended to suck gun fumes and blow them out through a hole in the right rear of the turret. The ammunition arrangement was reallocated. 27 shells would be stowed in the right and 13 in the left of the turret bulge. The 9 ready racks were switched in position, with 7 shells on the right and 2 on the left side of the turret. The remaining shells and charges would be stored on the hull floor inside an armored rack. The whole complete ammunition load weighed about 2.2 tons (2.08 tonnes).

Due to the favorable results from variable power sighting telescopes and the request for the standardization of the T122 as the M83 telescope for issue to tanks and tank destroyers armed with high-velocity guns, a project was initiated to develop a bigger telescope designed for the T29. The substitute M70E2 telescope that was carried over from the M6A2E1 was replaced by the new scope, designated as T143E1.

The tank’s weight increased significantly from 59 ½ tons (54 tonnes) to almost 68 tons (62 tonnes). This crippled any common transportation methods, as there was no adequate bridge capable of supporting the T29. The widened Bailey–type triple–double panel bridge would carry the tank over a maximum span of 110 feet (33.5 m) width. However, this bridge was under procurement and none were ready in stock yet. Heavy floatation bridges and dry ferries for up to 79 tons (72 tonnes) of loading were undergoing development, and expected to arrive by the end of 1945 (OCM 26825). A new 30 inch (762 mm) wide steel track, designated T93, was being developed and expected to replace the T80E3 track currently used by the T29. A reason for this change was that T80E3 was an asymmetric type of track, a combination of T80E1 and Duckbill extended end connectors, and therefore, not considered sufficiently robust or reliable.

The new rounds in development for the T5E1 gun were designed to replace the substitute rounds of the T4 gun, including AP, HE, and APCR. The T32 was a solid APCBC projectile weighing 39 pounds (17.7 kg), capable of penetrating heavy armor at high obliquity. The shell design had been completed, and it was anticipated that the performance would surpass the earlier T13 round.

At the same time, work on improving the T13 progressed mainly in heat treatment, in which early batches of T13 shells were considered unsatisfactory. Newly redesigned shells with the improvements were the T13E1, T13E2, and T13E3. The T13E1 was tested and resulted in sufficient performance in both the design and the heat treatment against 102 mm and 127 mm face-hardened armor plates at 20°. The T13E2 had a thinner cap and was made from WD–9465 steel, and reported to be superior to the earlier T13E1 against face-hardened armor. The furthest of the T13 design, the T13E3, differed with a single radius on the projectile body and reduced diameter explosive cavity, was produced from WD–4370 steel. Aberdeen conducted tests with both T13E2 and T13E3 against various homogeneous and face-hardened plates for comparison, and concluded that the T13E2, with its better heat treatment, was still superior to the T13E3.

A new T30 HE shell was being designed to replace the T12 HE that originated from the 105 mm T4 ammunition, designed to work at both high velocity for achieving maximum range of attack and low velocity against hardened structures. High Velocity Armor–Piercing shot (HVAP) was the latest of the 105 mm weapon development, intended to create a more effective anti–armor ammunition than the regular AP shot. The shell designated as T29 consisted of a tungsten core contained in a magnesium body fitted with a steel bourrelet band, magnesium ballistic cap, and a steel base with copper driving band. Up to four designs were made; T29 (7.9 lbs/3.6 kg core), T29E1 (9.9 lbs/4.5 kg core), T29E2, (12 lbs/5.4 kg core), and T29E3 (9.9 lbs/4.5 kg core). The latter round was a redesign of the T29E1 that was 2.8 pounds (1.3 kg) lighter (estimated weight around 24 lbs/11.1 kg).

Procurement of the Heavy Tank T29 was reduced, from 1200 vehicles to 1152 in April, with the approval of production starting next year (OCM 27331). 6 pilots were planned for construction in total (OCM 27245). The first pilots of the T29 heavy tank hull and turret were being constructed in July and expected to be completed in the same month.

The T29 was classified as “B” type heavy tank, indicating heavier type than the preceding “A” type heavy tank of the T26 series. At the time of the writing of this report, 6 pilots were planned for development with two in manufacturing, with subsequent production vehicles following up later. Source: AFV Technical Situation Report No. 36.

With the end of hostilities on the European front in May 1945, the production of T29s under the request from OCM 27331 was suspended as the heavily armored opposition that the T29 was designed to combat in Europe had already been defeated, leaving Japan as the sole threat. Amphibious operations against the Japanese forces were dangerous due to the coastal defense guns located inside heavy bunkers. The firepower of the 75 mm, 76 mm, and 90 mm cannons already available would not be able to damage their reinforced structures significantly. Seeking the advantages of using the 105 mm cannon of the heavy tank for this purpose, T29 resumed production in readiness for Operation Downfall, a planned large-scale invasion of Mainland Japan. Owing to the expectation of difficulty when traversing the mainland terrain with a tank weighing over 66 tons (60 tonnes), the development of the 30 inch (762 mm) wide T93 steel track was prioritized, although it was only on 1 July 1948 that the track would be completed and delivered to the T29 for testing. The track width had been reduced from the initial design to 24 inches (609.6 mm) during the development. It did not provide any substantial improvements over the asymmetric type T80E3 during the trials and the project was terminated in 3 September 1953.

The first T29 was finished in late July 1945 and located at General Motors’ Milford Proving Ground to provide data for the Detroit Transmission Division about its CD–850–1 cross–drive transmission. An equilibrator was installed to offset the added weight of the muzzle brake. The ammunition arrangement was redistributed again. 46 projectiles and 19 propellant charges would be stored in the turret, with the remaining ammunition stored in the hull. At the same time, the shell loadout for the T29 was standardized. Improved versions of the recently developed rounds would be made available for the gun to use; T32E1 APCBC, T29E3 HVAP, T30E1 HE, and a new burst–type white phosphorus smoke shell, designated as T46 WP.

The first T29 pilot finished at Milford Proving Ground in July 1945. Source: AFV Technical Situation Report No. 39.

After the end of the Pacific War, the production contract with Pressed Steel Car Company was terminated, with one pilot tank completed and a partially finished second pilot. All materials for the completion of 10 production tanks, including one partially finished pilot tank, were transferred to Detroit Arsenal for post-WWII development studies authorized by OCM 28848 on 23 August 1945. The first production T29 arrived at Aberdeen Proving Ground in October 1947. By this time, there was no longer any requirement for production of these heavy tanks and the test program was limited to evaluating the various power train components for application to new tank designs. Two additional T29s arrived in April and May 1948 for the endurance and engineering test programs. Ten tanks were built in total, two of which were the pilot vehicles built by Pressed Steel Car Company and eight were production tanks with the development continued by Detroit Arsenal. Some were modified independently to mount various experimental components such as new engine, fire control system, and stereoscopic rangefinder. This resulted in the development of T29E1, T29E2, and T29E3 heavy tanks that would test these new modifications.

The front and rear position of the T29 Pilot, September 1945. Source: Pressed Steel Car Company

The T29 project was discontinued in late 1950 in favor of a new heavy tank development based on the 120 mm cannon of the T34 in a new tank design, designated as T43 heavy tank, and standardized as 120 mm Gun Tank M103 in 1956.

Armor

The T29’s basis armor requirement of up to 228 mm of armor protection from frontal attack direction. Source: AFV Technical Situation Report No. 27.
The T29’s basis armor requirement of up to 228 mm of armor protection from frontal attack direction. Source: AFV Technical Situation Report No. 27.

The T29 was required to gain significant armor protection over the T26E3 Pershing. It was meant to be protected against the threat posed by the German high velocity cannons, notably the 8.8 cm Kw.K.43 high velocity cannon of the Tiger II. Basis armor thickness is the contemporary US term for what is today known as effective armor thickness. Necessary overhauls to both hull and turret protection were required beyond what the previous tank designs could offer, starting with 228 mm of basis armor requirement on the frontal projection.

U.S. Armor Basis Curve.
U.S. Armor Basis Curve.

Hull

The hull armor was a welded assembly of cast and rolled plates. The upper front glacis retained the 102 mm armor thickness from the Pershing, but with increased inclination to 54° to improve the basis armor thickness up to 228 mm, arranged with additional two rows of spare track links as a form of additional armor. A 7.62 mm machine gun port was stationed on the right side of the hull.

The proposed change of the upper front hull from 127 mm at 46° (same inclination as the Pershing’s front hull) to 102 mm at 54°, while maintaining basis armor equivalency of 228 mm.
The proposed change of the upper front hull from 127 mm at 46° (same inclination as the Pershing’s front hull) to 102 mm at 54°, while maintaining basis armor equivalency of 228 mm.

The lower front plate was 2.7 inches (70 mm) thick and angled at 58° at the center of the plate. The sides were split into two sections, 3 inches (76 mm) covering the fighting compartment and 51 mm covering the engine compartment toward the rear hull. The roof armor was .9 inches (25 mm) around the turret and half an inch (13 mm) above the engine deck.

  • Front, upper : 4 inches (102 mm) @ 54°
  • Front, lower : 2.7 inches (70 mm) @ 58°
  • Side, front : 3 inches (76 mm)
  • Side, rear : 2 inches (51 mm)
  • Rear : 2 inches (51 mm)
  • Roof, front : .9 inches (25 mm)
  • Roof, rear : ½ inch (13 mm)
  • Floor, front : .9 inches (25 mm)
  • Floor, rear : ½ inch (13 mm)

Turret

The variable armor thickness of the turret started at 6.2 inches (158 mm) at the front, tapering to 5 inches (127 mm) to the side of the loaders hatches, and 4 inches (102 mm) around the commander’s cupola and the rear of the turret. The turret roof armor consisted of 1.4 inches (38 mm) on the front and .9 inches (25 mm) on the rear.

A massive cast turret was welded on 78 inch (2 meter) wide turret ring and mounted a large gun mantlet at the front, covering a large portion of it. The thickness exceeded 8 inches (203 mm) on overall area, with up to 10 inches (254 mm) around the gun collar and 12 inches (305 mm) on the joints around the corner of the mantlet. An internal armored plate was attached to the gun mount as a secondary protection, forming the estimated 9 inches (228 mm) basis armor requirement on the frontal portion of the turret.

  • Mantlet : 8 – 12 inches (203 – 305 mm)
  • Front : 6.2 inches (158 mm)
  • Side : 4 – 6.2 inches (102 – 158 mm)
  • Rear : 4 inches (102 mm)
  • Roof : .9 – 1.4 inches (25 – 38 mm)
Heavy tank armor specification per August 1945. Source: AFV Technical Situation Report No.37, Appendix C.
Heavy tank armor specification per August 1945. Source: AFV Technical Situation Report No.37, Appendix C.

Weapon

In order to develop a tank with the firepower to assault enemy fortifications and heavily armored combat vehicles, particularly the German heavy tanks, it was important to mount a gun able to fulfill these multiple roles. As such, the 105 mm T5E1 was developed for the current U.S. heavy tank projects, T95 GMC and T29, with M6A2E1 becoming a test subject for feasibility of mounting the gun into a turreted tank design.

The 105 mm T5E1 was a 65 caliber long, high velocity multipurpose cannon based on the 105 mm T4 anti–aircraft gun, with a muzzle velocity of 914 m/s. The gun was made of a monoblock construction with uniform right hand rifling. It had a vertical sliding wedge breech block, with three recoil cylinders located on top of the gun cradle, installed on the T123 gun mount. Loading characteristics of the tank intended for installation demanded that the cartridge case and shell be separated as two–piece ammunition, with an effective rate of fire of 6 rounds/minute with 2 loaders. Another variant of the gun was the 105 mm T5E2, installed on the T123E1 gun mount. The only key difference was the relocation of one recoil cylinder to the bottom of the gun cradle.

The T29 could store up to 63 rounds, located in an armored rack in the hull and a ready rack in the turret. Ammunition types comprised the T13E2 APCBC–HE, T29E3 HVAP, T30E1 HE, T32E1 APCBC, T37 APBC, and T46 WP. Most of the 105 mm shells were rescaled from 90 mm shells, with the exception for the T13E2, which was based on the 75 mm M61 due to being developed much earlier for the T4 gun. Two separate propellant charges were provided, T8 for AP shot, HE, and WP shells, and T9 specifically for HVAP shot (with finer powder granulation). Both charges were assembled with the same cartridge case and components, namely 105 mm Case T4E1, Primer T48, Supplementary Igniter T9, and M1 Powder. The charges had been established to give a working pressure of 40,000 psi (2812.27 kg/cm²). Each cartridge case was closed by differently shaped plastic plugs, with flat contour for the T8 and convex contour for the T9 (to fit the recessed base of the HVAP projectile) to prevent mistakes in loading the separate projectile and charge.

105 mm T5 L/48 originally intended for tank use. The gun was somewhat 90 kg heavier than the 105 mm T5E1. Source: Watervliet Arsenal.
105 mm T5 L/48 originally intended for tank use. The gun was somewhat 90 kg heavier than the 105 mm T5E1. Source: Watervliet Arsenal.
105 mm T5E1 L/65. Source: Watervliet Arsenal.
105 mm T5E1 L/65. Source: Watervliet Arsenal.

The main cannon was complemented with two coaxial 12.7 mm M2HB machine guns, and a dual power telescope T143E1 in T154 telescope mount, adjustable from 4x to 8x of magnification. It was based on the T122/M83 telescope used for the 90 mm cannon. A secondary M10E5 periscopic sight with dual sights from 1x to 6x was provided for the gunner to give a wide angle of vision and acquire the target. Gun elevation/depression was +20/–10, and the turret was rotatable to 360° with an effective turret rotation of 18°/second.

The T143E1 telescope would have a similar sight to the M83 telescope, adjusted for the 105 mm cannon. Source: TM 9-735 - Medium Tanks M26 & M45.
The T143E1 telescope would have a similar sight to the M83 telescope, adjusted for the 105 mm cannon. Source: TM 9-735 – Medium Tanks M26 & M45.

The T13E2 APCBC–HE was the earliest anti–tank shell in development, carried over from the T4 AA gun. It had a muzzle velocity of 900 m/s, weighing 18.6 kg. It was a rescaled 75 mm M61 APCBC–HE. The fuze was a standard U.S. armor–piercing high explosive B.D. (Base Detonating) M66A1. It could penetrate 208 mm of vertical armor at 500 yd (457 m) and 180 mm at 2,000 yd (1,829 m).

The second armor–piercing shell was the T32E1 APCBC, a solid shot for the T5E1 after the T13E2 was developed. The base shell weighed 15.8 kg with 1.9 kg of hardened penetrating cap and steel ballistic cap, totaling 17.7 kg in overall, coming at a slightly higher velocity of 914 m/s. The third shell was the T37 APBC. It was not much different from the T32E1, as both were based on the same shell, the 90 mm T33 APBC. However, the T37 was a fully rescaled 90 mm, with the whole body and ballistic cap alone weighing 17.6 kg of similar size as the T32E1. Both APCBC and APBC could penetrate up to 235 mm and 216 mm of vertical armor from point blank range respectively.

T30E1 HE consisted of a cast TNT explosive packed inside a forged steel body shell with bursting charge and P.D. (Point Detonating) M51A4 fuze, weighing 15.4 kg in total. It came with two different charges, standard charge T8 for use at maximum range firing at 945 m/s, and reduced charge T20 for increased anti–concrete performance from short range at 762 m/s. It could penetrate 1.3 m of concrete at 1,500 yards (1,372 m).

High Velocity Armor–Piercing T29E3 provided the most effective anti–tank munition for the 105 mm. Weighing 11.2 kg, it consisted of a 4.5 kg tungsten carbide core, an aluminum ballistic cap and body with steel bourrelet band, and a steel base with two rotating bands and a tracer holder. It could achieve a muzzle velocity of 1,128 m/s, and penetrate 360 mm of vertical armor from 500 yd (457 m) and 292 mm from 2,000 yd (1,829 m). This was enough to punch through even the most heavily armored tanks in the war, including the Panzerjäger Tiger Ausf. B, colloquially known as the Jagdtiger heavy tank destroyer.

Armor-piercing performance of the 105 mm T13 APCBC and T29 HVAP. Source: AFV Technical Situation Report No. 34, Appendix D.
Armor-piercing performance of the 105 mm T13 APCBC and T29 HVAP. Source: AFV Technical Situation Report No. 34, Appendix D.

Mobility

The T29 was powered by the Ford GAC, a 12–cylinder petrol engine producing 750 hp at 2,800 rpm, with a maximum torque of 224.6 kgf/m. It had a displacement of 27 liters. Weighing 825 kg dry, it was connected to tanks with a fuel capacity of 300 U.S. gallons (1135 litres), running on 80 octane fuel and equipped with a liquid–cooling system. This gave the 64-ton heavy tank a power-to-weight ratio of 11.68 hp/t. The GAC engine was 35.5 cm longer than the GAA engine that powered the M4A3 medium tank, necessitating a larger engine compartment to fit such a machine.

Ford GAC engine. Source: AFV Technical Situation Report No. 25.

A General Motors Cross–Drive CD–850–1 transmission was connected to the Ford GAC. It combined the functions of a transmission, steering gear, and brakes in a single unit. This unit also incorporated two hydraulically selected gear ranges driving through a single phase torque converter. It had 2 forward and 1 reverse speed steering. The great advantage of the cross drive transmission was its simplicity of operation which eased the task of the driver. The top speed of the T29 was 35 km/h with a maximum cruising range of 160 km. It could climb 30° of sloped terrain, cross a trench up to 2.4 meters wide, ford depths up to 1.2 meters, climb steps up to 1 meter, and was capable of pivot steering by pushing the driver’s wobble stick to the left or right in neutral position, increasing the ability of the tank to exit from difficult terrain.

General Motors Cross–Drive CD–850–1 transmission schematic. Source: AFV Technical Situation Report No. 33.
General Motors Cross–Drive CD–850–1 transmission schematic. Source: AFV Technical Situation Report No. 33.
Assembled Ford GAC and GM CD–850–1 Powerpack. Source: Firepower
Assembled Ford GAC and GM CD–850–1 Powerpack. Source: Firepower

The suspension system was retained from the T26E3 Pershing, with 8 double road wheels with rubber tires connected to torsion bars and 7 return rollers per side. The drive sprockets were placed at the rear, as well as the transmission and the engine powering them, while the idler wheels settled at the front to keep the track tension. The T29 used as many as 102 links of T80E3 tracks on each side, a combination of 584 mm wide T80E1 rubber–backed, steel chevron tracks fitted with 127 mm wide Duckbill extended end connectors, increasing the total width up to 711 mm to reduce the ground pressure of the heavy tank to 0.85 kg/cm². The tank had a ground clearance of 480 mm.

Capt. W. (Bill) Day in front of the T29 Pilot, showing the 8 road wheels and 7 return rollers on the left side of the hull. Note the lack of Duckbill extended end connectors. Source: Pressed Steel Car Company
Capt. W. (Bill) Day in front of the T29 Pilot, showing the 8 road wheels and 7 return rollers on the left side of the hull. Note the lack of Duckbill extended end connectors. Source: Pressed Steel Car Company

Crew

The T29 was operated by a 6–man crew. Inside the turret, the tank commander was seated in the rear bulge immediately behind the 105 mm gun breech. He was provided with an M15 periscope and 6 vision blocks in his cupola. His seat could be adjusted vertically and horizontally for observation and movement. The SCR 508 / 528 radio set was installed in the turret bulge on the left side of the commander for intercom. Two loaders were stationed on each side of the breech, provided with two standard type escape hatches. Both had access to their ready racks located on both left and right side of the turret. When not in loading operation, the right loader could use a single pistol port on his side, while the left loader could use a 12.7 mm machine gun placed outside of the tank. The gunner manned the 105 mm gun and was located to the right of it, sitting on a seat slung from the turret ring, and equipped with a direct sight telescope and a periscopic sight. The driver and co–driver sat in the front hull and used M13 driver periscopes installed on their hatches for driving. Both had access to separate controls, including a mechanical control system to operate the transmission under normal conditions and two manual steering levers for emergency use.

Commander’s seat (left) and driver’s seat (right). Source: Pressed Steel Car Company

Variants

T29E1

The first production T29 completed by Detroit Arsenal was delivered to General Motors for installation of a different engine, the Allison V1710–E32, producing 850 hp at 2,800 rpm, and the CD–850–1 cross drive transmission. The hull length was slightly increased by 5 cm to accommodate the new engine installation. This modification was designated as T29E1 in December 1945.

Allison V–1710–E32 engine with CD–850–1 transmission. Source: Firepower
Allison V–1710–E32 engine with CD–850–1 transmission. Source: Firepower

T29E2

The second production T29 was equipped with a combination of hydraulic power turret traversing and elevating mechanism and computing sight system developed by the Massachusetts Institute of Technology. It was designated as T29E2 in April 1948, and armed with a 105 mm T5E2 cannon in T123E2 gun mount.

T29E3

On 31 May 1945, the T29 became the subject of an evaluation for the effectiveness of the integrated fire control system. This followed the development of the T25E1 No. 13 with T31 stereoscopic rangefinder, by incorporating the latest modification, the T31E1, and T93E2 telescope in T136 periscope mount, designated as the T29E3 in mid–1948. Three new panoramic telescopes for indirect fire with the 105 mm gun were also installed: T141 for the T31E1 rangefinder, T144 for the T93E2 telescope, and T145 for the M10E5 periscope. The T141 and T144 were installed in the gunner’s periscopic sight mount and the T145 in the turret roof.

Development for a rangefinder-equipped T29 heavy tank planned in May 1945. Source: AFV Technical Situation Report No. 36 #185

The T31E1 rangefinder was a stereoscopic instrument with the base length of 9 feet (2.74 meters). It was not connected to the other fire control system, as it was operated manually by the tank commander to relay the range information using the control box below the rangefinder. The range and target lead data was transmitted by flexible shafting to the gunner for tracking the target. However, tests at Aberdeen Proving Grounds (APG) showed that backlash, as well as windup and binding of the flexible shifting, resulted in serious errors in the system. Although the rangefinder was particularly useful for spotting purposes. It also displayed the importance of a rangefinder to obtain a first strike capability beyond 1,000 yards (914 m).

The T29E3 heavy tank at Aberdeen Proving Ground on 4 May 1948. The T31E1 rangefinder appeared on each side of the turret. Source: Firepower
The T29E3 heavy tank at Aberdeen Proving Ground on 4 May 1948. The T31E1 rangefinder appeared on each side of the turret. Source: Firepower

Turbine–Powered T29

In 1946, the T29 was planned for a gas turbine engine development program with the associated power train, estimated to produce up to 1,400 hp. The project was separated into three different phases; Researching the development data of the internal combustion turbines and power train suitable for the T29, developing a pilot gas turbine engine based upon the data derived in Phase 1, and installation of the engine into the T29. No further details have been revealed.

Plan to research gas turbine engine for the T29 heavy tank. Source: AFV Technical Situation Report No. 42 #94.
Plan to research gas turbine engine for the T29 heavy tank. Source: AFV Technical Situation Report No. 42 #94.

Conclusion

The T29 was developed too late to enter the war it was designed for, with the first tank finished at the end of hostilities in the Pacific War. The lack of preparation of any practical solutions to transport such massive vehicles overseas also contributed to its delay. However, all the equipment and modules that were developed during World War II would later pave the way for future American tanks. The cross-drive transmission was improved and later used by all subsequent tanks, up to the M60 main battle tank. The 105 mm T5E1 gun and its ammunition were adapted for post-war development and later known as the 105 mm T140 gun, installed on the T54 medium tank. The heavy tank project itself led to the development of the T43, and eventually to the M103 gun tank.

Production T29 at the Pressed Steel Car works, 1947. Source: Pressed Steel Car Company
Production T29 at the Pressed Steel Car works, 1947. Source: Pressed Steel Car Company

There are currently seven surviving tanks, four of which are located at the National Armor and Cavalry Museum, including T29, T29E3, T30, and T34. The remaining 3 are the T30s, located at Fort Jackson, Detroit Arsenal, and Anniston Army Depot.



Illustration of the Heavy Tank T29 showing the large size of the turret and the impressive size of the gun.


Illustration of the Heavy Tank T29E3 showing off the distinctive paraxial rangefinder on the top of the turret. These were used to quickly determine the distance to an enemy tank and improve the first hit chances.

Both illustrations were produced by Tank Encyclopedia’s own David Bocquelet

Specifications

Dimensions (L-W-H) 7.6 (11.6 m with gun forward) x 3.8 x 3.2 meters
Total weight, battle-ready 64.2 tonnes
Crew 6 (commander, driver, gunner, loader, loader, bow gunner)
Propulsion V12 Ford GAC, gasoline, 750 hp
Range 160 km
Speed (road) 35 km/h
Transmission CD–850–1, torque converter, 2–forward/1–reverse
Suspension Torsion bar
Armament 105 mm T5E1 L/65, 63 rounds
3x 12.7 mm M2HB, 2,420 rounds
1x 7.62 mm M1919A4, 2,500 rounds
Armor Hull
Front: 70 – 102 mm
Side: 76 – 51 mm
Rear: 19 – 51 mm
Roof: 13 – 25 mm
Floor: 13 – 25 mm
Turret
Front: 158 mm
Side: 158 – 102 mm
Rear: 102 mm
Roof: 25 – 38 mm
Mantlet: 203 – 305 mm
No. Built 10 (2x Pilot T29, 5x Production T29, 1x T29E1, 1x T29E2, 1x T29E3)

Sources

British Army Staff – AFV Technical Situation Report No. 23, June 1944
British Army Staff – AFV Technical Situation Report No. 25, August 1944
British Army Staff – AFV Technical Situation Report No. 27, October 1944
British Army Staff – AFV Technical Situation Report No. 28, November 1944
British Army Staff – AFV Technical Situation Report No. 29, December 1944
British Army Staff – AFV Technical Situation Report No. 30, January 1945
British Army Staff – AFV Technical Situation Report No. 31, February 1945
British Army Staff – AFV Technical Situation Report No. 32, March 1945
British Army Staff – AFV Technical Situation Report No. 33, April 1945
British Army Staff – AFV Technical Situation Report No. 34, May 1945
British Army Staff – AFV Technical Situation Report No. 35, June 1945
British Army Staff – AFV Technical Situation Report No. 36, July 1945
British Army Staff – AFV Technical Situation Report No. 37, August 1945
British Army Staff – AFV Technical Situation Report No. 38, September 1945
British Army Staff – AFV Technical Situation Report No. 39, October 1945
British Army Staff – AFV Technical Situation Report No. 40, November 1945
British Army Staff – AFV Technical Situation Report No. 41, January 1946
British Army Staff – AFV Technical Situation Report No. 42, March 1946
Armed Services Technical Information Agency – AD301343 – An Analytical Study of Data on Armor Penetration by Tank–Fired, Kinetic Energy Projectiles
Nielsen, K. (2012). Pressed Steel Car Company, Authorhouse
OCM 25117 – Heavy Tanks T29 and T30 – Development and Manufacture of Pilots Recommended, 14th September 1944
OCM 25259 – Tanks, Heavy, T29 and T30 – Development and Manufacture of Pilots Approved, 28th September 1944
OCM 26438 – Gun, 105–mm, T5E1 for Mounting in Tank, Heavy, T29 – Assignment of Model Designation, January 1945
OCM 26439 – Fire Control Equipment for the Heavy Tank T29 – Development and Assignment of Designation
OCM 26825 – Tank, Heavy, T29 – Classification as Limited Procurement Type Recommended; Gun, 105–mm T5E1 and Ammunition Therefor – Initiation of Procurement Recommended, 1st March 1945
OCM 27245 – Tanks, Heavy, T29 and T30 – Procurement of Additional Pilots Authorized, 5th April 1945
OCM 27808 – Gun, 105 mm, T8 and Carriage, Gun, 105 mm, T19, Fire Control Equipment; Accessories, and Associated Equipment, 31st May 1945
Records of the Office of the Chief of Ordnance – Development History of the Heavy Tanks, T29 & T30, 1945
R.P. Hunnicutt (1988). Firepower: A History of the American Heavy Tank


Tanks Encyclopedia Magazine, #3

Tanks Encyclopedia Magazine, #3

The third issue covers WW1 armored vehicles — Hotchkiss Htk46 and Schneider CA and CD in Italian Service. WW2 section contains two splendid stories of the US and German ‘Heavy Armor’ — T29 Heavy Tank and Jagdtiger.

Our Archive section covers the history of early requirements for the Soviet heavy (large) tank. Worth mentioning, that the article is based on documents never published before.

It also contains a modeling article on how to create a terrain for diorama. And the last article from our colleagues and friends from Plane Encyclopedia covers the story of Northrop’s Early LRI Contenders — N-126 Delta Scorpion, N-144 and N-149!

All the articles are well researched by our excellent team of writers and are accompanied by beautiful illustrations and photos. If you love tanks, this is the magazine for you!
Buy this magazine on Amazon!


Categories
WW2 American Prototypes

Heavy Tank T26E5

USA (1945)
Assault Tank – 27 Prototypes

The T26E5 was an assault tank based on the M26 Pershing heavy tank. It was developed from the same premise as the M4A3E2 Assault Tank, that of increasing the armor of the current existing tank with a purpose to break through the enemy defense line. The tank sported the same 90 mm Tank Gun M3 L/53 high-velocity cannon with heavily reinforced frontal armor.

The first T26E5 heavy tank (serial number 10007) at Aberdeen Proving Ground (APG) on 20 July 1945. Source: Hunnicutt’s Pershing

Development

With the rapid increase of enemy high-performance anti-tank firepower on the battlefield during WWII, the American primary tank, the M4 Sherman, found itself in a difficult situation where it could not protect the mobilizing forces anymore. Its existing design could not be pushed further to emphasize armor without hampering the other aspects of the tank, such as mobility. Therefore, a new role was formed to counter this threat, the Assault Tank, a vehicle with the purpose of breaking through highly concentrated enemy defenses and withstand enemy gunfire.

Successful deployment of the M4A3E2 in late 1944 had garnered interest in the US Army to develop another type of assault tank. While the M4A3E2 was considered satisfactory for its role, it did not provide nearly the same level of protection offered by its contemporaries, such as the German Tiger II. Fortunately, the heavy frontal armor arrangements of the M4A3E2 suggested the possibility of improving the armor for the latest heavy tank under production, the T26E3 Pershing. The earliest draft was recommended by the Ordnance Committee of the Ordnance Corps to increase the effective frontal armor of the Pershing by 203.2 mm. This entailed:

  • A new front hull casting with a maximum thickness of 120.65 mm at 46°.
  • A new turret casting with an effective thickness of 203.2 mm and a counterweight at the rear of the turret.
  • A new gun mantlet casting with an effective thickness of 203.2 mm at 0°.
  • Increased equilibrator capacity to offset the weight of gun mantlet.
The second T26E3 Pershing (serial number 12) heavy tank at APG on 12 December 1944. Source: Pacific Area Materiel

A rough estimation indicated that these changes would increase the vehicle weight to 48 tons (43.9 tonnes), 2.4 tons (2.2 tonnes) heavier than the T26E3. However, by using the T80E1 track with the Duckbill extended end connectors, it was expected that the ground pressure could be kept down to approximately 11 psi (0.80 kg/cm²). The overall width of the tank would be 12.3 feet (3.75 m), but could be reduced to 11.4 feet (3.5 m) for rail transportation. The tank would continue to be powered by the Ford GAF engine with Detroit 900-F torqmatic transmission. The gear reduction had to be lowered to maintain support of the increased tank weight. Dated 18 January 1945, an Ordnance Committee Minute (OCM) action recommended 10 conversions of the T26E3 tanks and designated the modified vehicles as Heavy Tank T26E5 under OCM 26398. This action was approved on 8 February.

A concept of the M4A3(90) HVSS with T26 turret. Source: Sherman

In order to gain information of the new assault tank, along with the performance of the High Volute Spring Suspension (HVSS) for a possible new assault tank using this type of suspension, a trial vehicle entered Utica Proving Ground in early 1945. The vehicle was a modified M4A3 HVSS hull loaded with test weight, and mounting a heavied-up T26 turret with the 90 mm M3 cannon. The overall weight of this trial assault tank was 46.26 tonnes. The M4A3(90) HVSS ran a 2,000 miles (3,218 km) test with this assault tank weight configuration for an endurance test.


The Assault Tank M4A3(90) HVSS, weighing 46.26 tonnes, being used to conduct a 2,000 miles test. Unfortunately, there is no existing photograph of such a tank during the test. Source: AFV Technical Situation Report No. 32

Following the information gathered from the trial assault tank, on 29 March 1945, the specification requirement was updated. OCM 27122 recommended increasing the weight limit of the T26E5 to 51 tons (46.26 tonnes) as well as the effective frontal armor thickness to 11 inches (279.4 mm) to exceed any heaviest known enemy armor. Proposed changes included the use of:

  • A new hull casting with a thickness of 6 inches (152.4 mm) at 46° on the upper slope and 4 inches (101.6 mm) at 54° on the lower slope.
  • A new turret casting with a thickness of 7 ½ inches (190.5 mm) on the front, 3 ½ inches (88.9 mm) on the sides (later changed to 95.25 mm), and 5 inches (127 mm) on the rear in order to balance the turret.
  • A new gun mantlet casting with the actual thickness of 11 inches (279.4 mm) at 0°.
  • A 59 lb (27 kg) counterweight to the recoil guard in addition to the increased equilibrator capacity for complete balance to the gun mount.
  • Increased thickness and weight of the front turret ring splash guard to protect the thin machined surface of the turret adjacent to the ring.
  • Decreased width in the rear portion of the hull escape hatch doors to prevent a weak spot in the turret and to provide clearance between the doors and the turret.
  • Reduced final drive gear ratio from 1:3.95 to 1:4.47.

The Chief of Engineers pointed out that the gross weight and width of the assault tank would place it under the classification of “Exceptional Vehicle”. The only military bridging available which would safely carry it was the Floating Bridge M4. With the bridge width of 12 feet (3.75 m), it could merely afford a clearance for the tank when not equipped with extended end connectors. Regardless, OCM 27122 was approved on 19 April 1945 and the production number for T26E5 had been increased to 27.

As of 10 April, marked prints covering the alterations to the front hull casting, turret, gun mantlet, driver’s door, and the equilibrator spring had been completed. The casting drawings had been delivered to the Scullion Steel Co. and the Continental Foundry and Machine Co. for the production of 27 vehicles, which were to be built by the Chrysler Corp. Production drawings for all other parts related to the vehicle were being made and it was expected that the first tank would be completed by approximately 15 June 1945.

Schematics of T26E5 Heavy Tank. Source: AFV Technical Situation Report No. 35

Meanwhile, a modification unit to the suspension was being worked out in the event that such changes were necessary to carry the unprecedented weight of the tank. These involved increasing the diameter of torsion bars to 23.6 in (60 cm) which would increase their range by 15%, larger inner road wheel bearings to increase the capacity to 80% over the existing bearings on the T26E3. Strengthened shock absorbers and an extra shock absorber, together with a hydraulic bump stop were to be provided on the front suspension member. But none was really installed into the tank, which would bring out the issues of its suspension reliability later in trials.

The first T26E5 (registration number 30150824) arrived at Aberdeen Proving Ground (APG) in July 1945. The final combat weight of the vehicle was measured at 46.40 tonnes, slightly heavier than estimated. All the remaining tanks had finished production by the end of World War II, and no additional unit was ordered.

The T26E5 heavy tank arrived at APG in July 1945. Source: Pacific Area Materiel

Armor

As an assault tank, the T26E5 was heavily armored, far beyond any preceding assault tanks developed by the US. With a maximum effective armor of 279.4 mm, it outclassed even the T29 heavy tank, one of the latest US heavy tanks which was already in production 3 months prior. Unlike the other T26 variants which had lower effective armor on the front hull, the T26E5 was designed to project its maximum armor on the entire front, including the hull and the front turret that was covered by the mantlet. Preliminary study to incorporate the required effective armor into the tank construction was done by measurement using the standards of US Basis Armor Curve. Since most of the changes to protection were allocated to the front, the side and rear of the hull were left without any relevant changes at all.

Final armor specification of the T26 heavy tanks. Source: AFV Technical Situation Report No.33

Hull

The armor structure was relatively similar to the M26 Pershing, with cast and rolled armor forming up the hull. The main aspect of the T26E5 armor came from thicker casting of the front hull, coming up at 6 inches (152.4 mm) at 46° on the upper slope, giving a substantial effective thickness of 11 inches (279.4 mm). The ventilator bulge located above the upper slope was angled at lower obliquity at 25°, and to provide the same protection as the upper slope, the armor plating must be cast thicker than the rest of the upper front hull with an estimation of 9 ½ inches (242.9 mm) at its thickest. The lower plate was also well armored with 4 inches (101.6 mm) at 54° at the center of the lower slope. The side hull was split with 3 inches (76.2 mm) on the front and 2 inches (50.8 mm) on the rear. The rear hull was 2 inches all around the engine compartment.

  • Front, upper: 6 in (152 mm) @ 46° CHA
  • Front, lower: 4 in (102 mm) @ 54° CHA
  • Side, front: 3 in (76 mm) RHA
  • Side, rear: 2 in (51 mm) RHA
  • Rear: 2 in (51 mm) RHA
  • Roof, front: 1.5 in (38 mm) RHA
  • Roof, rear: 0.90 in (23 mm) RHA
  • Floor, front: 1 in (25 mm) RHA
  • Floor, rear: ½ in (13 mm) RHA
A thickness of 6” (152.4 mm) CHA angled at 45° or 4” (101.6 mm) at 51° was required to defeat the German 8.8 cm Kw.K. 43 cannon at point-blank distance. The front hull construction of T26E5 was based upon this information. Source: AFV Technical Situation Report No.34

Turret

The turret was cast all-around, and received a sizable overhaul to its protection, with 7 ½ inches (190.5 mm) at 10° on the front turret giving an effective armor of 8 inches (203.2 mm), and 11 inches of effective armor on the mantlet. The sides had varying degrees of thickness due to casting from 7.8 in (198.12 mm) on the front, which was actually thicker than the front turret face, and tapering down to 3 ½ inches (88.9 mm) on the rear. The rear section of the turret was thickened to 5 inches (127 mm) to balance the weight of the heavily armored mantlet at the front of the turret.

The mantlet shape was improved by trimming a chunk of its lower portion in an attempt to form a straight surface instead of rounded. This offered three advantages: preventing shot trap that was noted to be a serious compromise in the previous design since the T26E1; allowing the drivers hatches to open since the mantlet became thicker externally; and permitting enough space for the gun mount to traverse vertically without bumping into the driver hatches.

  • Mantlet: 7 ½ – 11 in (191 – 279 mm) CHA
  • Front: 7 ½ – 7.7 in (191 – 198 mm) CHA
  • Side: 3 ½ – 7.7 in (89 – 198 mm) CHA
  • Rear: 5 in (127 mm) CHA
  • Roof: 1 in (25 mm) CHA
Cast turret armor of the T26E5 inspected at APG on 16 July 1945. Chalked numbers indicate armor thickness in inches. The front turret face has a thickness of 7.5 inches (190.5 mm). The sides of the turret vary from 7.8” (198.12 mm) on the front to 3.5” (88.9 mm) on the rear. Source: Pershing

Weapon

The T26E5 still used the same weaponry as the M26 Pershing, with no notable differences. The main gun was the 90 mm M3 L/53 cannon, holding 70 rounds of 90 mm ammunition consisting of M71 HE (High Explosive), T33 APBC (Armor-Piercing Ballistic Capped), M82 APCBC-HE (Armor-Piercing Capped, Ballistic Capped, High Explosive), M304 HVAP (High Velocity Armor-Piercing), and M313 WP (White Phosphorus / Smoke). The secondary weapon would be a coaxial .30 caliber (7.62 mm) M1919A4 machine gun on the left side of the cannon. Additional machine guns included a ball-mounted .30 caliber M1919A4 for the bow gunner and .50 caliber (12.7 mm) M2HB heavy machine gun in a flexible anti-air mount on top of the turret.

The first T26E5 heavy tank as seen from above, showing the 90 mm M3 cannon and anti-aircraft .50 cal M2HB machine gun The .30 cal M1919A4 coaxial machine gun was not visible, shrouded by a mantlet canvas cover to prevent dust from entering the gun mount. Source: Hunnicutt

Although using the same M67 Gun Mount type as the Pershing, it was modified with significantly thicker mantlet and increased equilibrator capacity, gathered from experience with the T26E4 Super Pershing to maintain balance of the whole platform with the increased weight at the front of the turret. Despite projecting such a large mantlet, the gun mount was still able to elevate 20° up and depress -10° down. The turret rotation speed was reduced to 18°/second since the turret became heavier.

The 90 mm cannon of the T26E5 was initially planned to use the M71C telescope with fixed 5x (13°) magnification, backed up by the M10F periscope with 1x (42° 10’) infinity sight and 6x (11° 20’) telescopic sight. Although in June 1945, the M83C variable power telescope became available after being standardized and authorized for mass production. Naturally, the T26E5 would immediately adopt it somewhere during production, replacing the M71C in process. This new power telescope was capable of veritable magnification from 4x (14° 27’) to 8x (7° 36’) and had better resolution and optical quality than any previous telescopes. The telescope mount on the mantlet was given a cylindrical cover since the telescope would extend by up to 3.8 cm when magnified to 8x.

The Telescope T122 was a variable telescopic sight developed since March 1944. It was not until June 1945 that the telescope was standardized as Telescope M83. The T26E5 in particular was among the first tanks to adopt the M83C model. This telescope had a magnification ranging from 4x to 8x. Source: AFV Technical Situation Report No.29

Mobility

The heavy tank was still powered by the same power pack as on the M26 Pershing, including the Ford GAF gasoline engine producing 500 hp, which was proven to be underpowered for the tank at just 45 tons (41 tonnes). It should have been expected that the T26E5 that weighed just over 50 tons (46 tonnes) would suffer even more from reduced performance, with abysmal power-to-weight ratio giving an output of only 10.7 hp/ton. The Detroit 900-F Torqmatic transmission was also still used, with a change to the final drive ratio from 1:3.95 to 1:4.47. The top speed had been limited from 30 to 24 mph (48 – 40 km/h). The T26E5 used 23 inch (584 mm) wide T80E1 rubber-backed, steel chevron tracks. There were 82 track links used on both sides, each fitted with Duckbill extended end connectors to reduce the ground pressure from 14.3 to 11.8 psi (1.01 – 0.83 kg/cm²). It could climb up to 30° of sloped terrain, cross a trench up to 7.8 feet (2.4 m) wide, ford depths up to 3.9 feet (1.2 m), climb steps up to 3.9 feet, and turn with a maximum circle of 60 feet (18.2 m) in diameter.


The third T26E5 heavy tank (serial number 10009) during tests at Fort Knox. The Duckbill extended end connectors have been removed from the tracks and standard width sand shields fitted. This was necessary to reduce the overall width for rail transportation. Source: Pershing

Crew

The T26E5 was operated by a 5–man crew, just like the M26 Pershing. The commander, gunner, and loader were stationed inside the turret, while the driver and bow gunner settled down on the front hull.

In the turret compartment, the commander was located on the right side of the turret, and had access to his cupola with 6 vision blocks and a rotating periscope for all-directional observation while inside the tank. Behind him, a radio set was installed inside the turret bustle, either SCR 508 or SCR 528. The gunner was right in front of the commander, armed with the 90 mm cannon and .30 caliber coaxial machine gun at his disposal. Periscope M10F and Telescope M83C were available for him to locate and aim at the target. The loader sat on the left side of the turret, and had a ready rack of 10x 90 mm rounds beside him. The remaining ammunition was stored on the hull floor in an armored rack, which could still be accessed through the turret basket. The loader also had access to a pistol port, an escape hatch, and a rotating periscope.

Both the driver and bow gunner (as assistant driver) steered the tank with a pair of levers to their left and right, respectively. The instrument panel was located in the middle. On top of it, there was a blower to circulate air into the hull compartment. The bow gunner was armed with a ball-mounted .30 cal machine gun with no sighting device, so he had to aim the gun through his periscope and lead the firing direction by watching the tracer bullets. Two CO2 fire extinguishers were provided between their seats. The auxiliary periscopes had been eliminated from the M26 Pershing, leaving only rotatable periscopes on the hatches.

Conclusion

No longer needed for combat in World War II, the T26E5 was utilized for automotive and protection trials by the Service Board to study the effect of increased weight while running the same power pack and suspension as the M26. The consequence of weight increase by up to 5 tonnes would be a clear reduction to the mobility performance as estimated. The vehicle ran for another 2,000 miles (3,218 kilometers) test in the same principle as the M4A3(90) HVSS, to test the endurance of the tank. Unfortunately, due to the absence of the suspension modification unit that was supposed to alleviate the weight carrying capability of the T26E5, the test resulted in numerous malfunctions occurring in each distance recorded:

  • 1,247 km: Left and right hand final drive lock washers failed.
  • 1,879 km: Front right road wheel hub was bent and damaged.
  • 2,199 km: A torsion bar broke at the right front of the hull.
  • 2,354 km: Engine was overheated due to oil and dirt clogging radiator.
  • 2,393 km: Front spring arm shackles were bent and bearings damaged.
  • 2,533 km: Complete power failure occurred, caused by shearing of the torque converter’s rotor blades.
  • 2,623 km: Second torsion bar broke at the left front of the hull.
  • 2,943 km: Speed band in the transmission broke at the point of connection to the link on the adjustment end.

Overloading of the light duty torsion bar originally designed for the M26 caused considerable issues to the suspension, with cases of broken bars occurring twice. The light duty torsion bar was not capable of taking the additional 5 tonnes of weight amassed by the T26E5. The turret operation also suffered from failures, especially during cross-country driving. The problem was traced to be a direct result of the increased turret weight by uparmoring from the entire side, as there was no visible defect to the turret assembly or the material quality.

As the engineering trials proved to be a failure due to the design flaws surrounding its excessive weight and inability of the modified M26 to overcome them, it was decided that the T26E5 would be useful with its heavy armor as a practice target. The target vehicle would be loaded with inert ammunition and wooden crew in each of their positions inside the tank, and a running engine. The vehicle would then be shot by live anti-tank munition to determine the weapon’s performance against the heavy armor of T26E5.

All the 27 tanks were either lost to gunfire tests or scrapped, and none survived.



Heavy Tank T26E5 “Assault Pershing” in the standard US Olive Drab livery in 1945.


Heavy Tank T26E5 No. 1, with registration number “0824” stenciled at the rear side of the turret. The .50 cal machine gun has been mounted on top of the tank for anti-aircraft emplacement. The mantlet is protected by canvas cover to keep the gun mount clean during trials at APG in July 1945.

Both illustrations were produced by Ardhya Anargha, funded by our Patreon campaign

Specifications

Dimesnions (L-W-H) 20 (28, gun forward) x 12.1 x 8.8 feet (6.3 (8.6) x 3.7 x 2.7 meters)
Total weight, battle ready 51 tons (46.6 tonnes) Aprx.
Crew 5 (commander, driver, co-driver, gunner and loader)
Propulsion Ford GAF V8, gasoline, 500 hp
Speed (road) 24 mph (40 km/h)
Transmission Detroit 900-F Torqmatic, torque converter, 2 forward, 1 reverse
Suspension Torsion bar
Armament 90 mm Tank Gun M3 L/53, 70 rounds
1x 12.7 mm M2HB, 550 rounds
2x 7.62 mm M1919A4, 5000 rounds
Armor Hull
Front, upper: 6 in (152 mm) @ 46° CHA
Front, lower: 4 in (102 mm) @ 54° CHA
Side, front: 3 in (76 mm) RHA
Side, rear: 2 in (51 mm) RHA
Rear: 2 in (51 mm) RHA
Roof, front: 1.5 in (38 mm) RHA
Roof, rear: 0.90 in (23 mm) RHA
Floor, front: 1 in (25 mm) RHA
Floor, rear: ½ in (13 mm) RHA
Turret
Mantlet: 7 ½ – 11 in (191 – 279 mm) CHA
Front: 7 ½ – 7.7 in (191 – 198 mm) CHA
Side: 3 ½ – 7.7 in (89 – 198 mm) CHA
Rear: 5 in (127 mm) CHA
Roof: 1 in (25 mm) CHA
No. Built 27

Sources

Ballistic Research Laboratories, Aberdeen Proving Ground – Critical Review of Shaped Charge Information, 1954
British Army Staff – AFV Technical Situation Report No. 30, January 1945
British Army Staff – AFV Technical Situation Report No. 31, February 1945
British Army Staff – AFV Technical Situation Report No. 32, March 1945
British Army Staff – AFV Technical Situation Report No. 33, April 1945
British Army Staff – AFV Technical Situation Report No. 34, May 1945
British Army Staff – AFV Technical Situation Report No. 35, June 1945
British Army Staff – AFV Technical Situation Report No. 36, July 1945
British Army Staff – AFV Technical Situation Report No. 37, August 1945
British Army Staff – AFV Technical Situation Report No. 40, November 1945
British Army Staff – AFV Technical Situation Report No. 41, January 1946
British Army Staff – AFV Technical Situation Report No. 42, March 1946
Office of the Chief of Ordnance – Pacific Area Materiel, 1945
Ordnance Corps – Engineering Design Handbook, Ammunition Series. Section 2, Design for Terminal Effects, 1957
Record of Army Ordnance Research and Development – Heavy Tanks and Assault Tanks, 1945
R.P. Hunnicutt (1971) – Pershing: A History of the Medium Tank T20 Series
R.P. Hunnicutt (1978) – Sherman: A History of the American Medium Tank

Categories
WW2 American Prototypes

Armored Utility Vehicle T13 and Cargo Carrier T33

USA (1944-45) Utility Vehicle – Prototypes

The T33 Cargo Carrier and T13 Armored Utility Vehicle were designed in the United States of America during the Second World War. The T13 and T33 occupy a space in development as transition vehicles in the sense that almost everything Armored Personnel Carrier related that comes before the T13 and T33 was adopted from other designs originally intended as artillery tractors, half-tracks, tanks or, mortar carriers. Although neither vehicle was adopted for mass production, much like those that preceded them, they set the standard and bar for future APCs on what was expected and needed of the vehicle.

Initial Development

The T33 Cargo Carrier and T13 Armored Utility Vehicle (the name was changed to this from Armoured Tracked Carrier) were first mentioned in August 1944 in the British Army Staff (AFV) Situation Report Number 25 from August 18th 1944. At the time, the Armored Board and Armored Centre were interested in a design of an Armored Tracked Carrier, eventually called T13, based upon the M24 Light Tank components. The proposal was for the driver and engine room to be at the front, followed by a body which would be capable of carrying a 13,000 lb (5,900 kg) payload. Its dimensions would enable 9 men to be carried in the body with an additional 2 in the driving compartment.
The armor over the hull of the chassis would be 1” (25.4 mm), whilst the body would be ½” (12.7 mm). The total weight of the vehicle was estimated at 40,000 lbs (18,143.69 kg). Such a Carrier was considered to be particularly desirable for acting as a tender for ammunition and fuel for the M24 Light Tank, which only carried 48 rounds, or as a personnel carrier, or command vehicle in theaters such as China, where the absence of roads placed a premium on tracked vehicles. As of August 18th, 1944, “a layout drawing only has been produced and support for the proposal is now being canvased.”
There were no fully tracked armored personnel carriers being produced anywhere in the world since the Mark IX tank of World War One and APCs based upon the Soviet T-26 in the early 1930s. Walking, trains, trucks, and increasingly, half-tracks were the primary ways to move troops. The Tank Policy for 1945, which was published in July 1944, laid out the main focus for the coming year in the European Theater of Operations (ETO), that focus being on Tanks carrying a minimum of 70 rounds of ammunition. Water stowage for these rounds to reduce the chances of fire was acceptable so long as no less than 70 rounds were carried. Ground pressure was not to exceed 10 psi (0.70307 kg/cm2) and tank design was to be split into two types, light armor and high mobility, and heavy armor and infantry support. The end result of the requirements from July 1944 was that the M4A3 Medium Tank and M24 Light Tank fitted the lighter requirements well. At the same time, while the T25E1 Medium Tank was considered, it was thought that it would negatively impact the production of the M4A3 Medium Tank and M24 Light Tank and, if it was introduced alongside the two tanks, it would not arrive in enough quantity to have any impact. The heavy role was to be filled by the T26E1 Heavy Tank, and both the light and heavy tank roles were supposed to be able to mount the 90 mm Gun and the 105 mm Howitzer.
In addition to the Tank Policy, the Army was in need of more tractors to haul towed guns of various calibers due to production of the M4, M5, and M6 Tractors (as well as Tractor Trucks) not being able to keep up with demand and the increasing production of towed gun carriages. The idea to convert M24 chassis into both Cargo Tractors and Armored Utility Vehicles was both sound and nothing new, as the idea had been previously considered and declined.

October 1944

By October of 1944, it had been expressed in overseas theaters of operation, that a definite need existed for a General Purpose Tracked Cargo Carrier with low unit track pressure (PSI) and effective cross-country performance over difficult terrain. To meet this requirement, Ordinance prepared a design for a new carrier with a 7-ton cargo (6.4-tonne) capacity identified as the T33 Cargo Carrier. The vehicle was to be built from standard M24 Light Tank components, be unarmored, have a crew of two, and a .50 cal machine gun for A.A. work manned by the assistant driver. The unit track pressure was to be 6 psi (0.42 kg/cm2). Six pilot vehicles were authorized, but as of October 1944, no manufacturing facility had been located. Also recommended for official investigation was the previously mentioned armored tracked carrier based off the T33, the T13, now called a Personnel Carrier which had been previously reported on back in August of 1944[4].


Images of the Cargo Carrier T33 from October 1944. Source: British Army Staff (AFV) Situation Report Number 27 October 18th 1944

In November of 1944, the T33 Cargo Carrier became better described as 24,000 lbs (10.9-tonnes) (less crew, stowage and fuel) and 39,000 lbs (17.7-tonnes kg) combat laden in a cab over engine design at the front of the chassis.
The T13 also got official recognition as the T13 Armored Utility Vehicle in which the truck cab body of the T33 was replaced with an armored body ½” (12.7 mm) thick on the front, ½” (12.7 mm) thick on the side and 3/8” (9.5 mm) thick on the roof. The roof was lifted by means of mechanical jacks which raised it to any required position up to 6 ft (1.83 m) above the floor. The driver’s compartment accommodated the driver and co-driver with a ring-mounted .50 caliber machine gun over the co-driver. The main body was designed to accommodate 16 men in four rows of four leaving a small central aisle. This vehicle was estimated to weigh 31,000 lbs (14-tonnes) (less crew, stowage and fuel) and 39,000 lbs (17.7-tonnes) combat laden with the ground pressure being 7.3 psi (0.51kg/cm2).
The base carrier design was also intended to be suitable as an a) Armored Personnel or Cargo Carrier, b) Full Track Armored Reconnaissance Vehicle, c) Gun Motor Carriage, d) Litter Carrier and e)Full Track Armored Prime Mover.
The B.A.S. Royal Artillery S.D. and T. (R.A.) Monthly Letter to the War Office(RA) for December 7th, 1944 notes that the T33 had been approved for the production of six pilot vehicles[8]. The Technical Services Armaments Letter (TSAL) for November 29th, 1944 also notes this. Curiously, the British Army Staff (AFV) Situation Report (BASSR) Number 28 for November 18th, 1944 makes no mention of the six pilots for the T13 and both the TSAL and RA reports do and both reports cite BASSR #27 from October 18th, 1944.
By February 1945 and as a result of several user criticisms, the wooden mockup for T13 Armored Utility Vehicle was undergoing modifications and was not yet complete. In addition, six prototype T13 Armored Utility Vehicles were still on order but no delivery dates had yet been established[9].


Armored Utility Vehicle as drawn in the British Army Staff (AFV) Situation Report from November 1944. Illustrated by Yuvnashva Sharma, funded by our Patreon campaign.

Drawings and scale model of the Armored Utility Vehicle T13 from November 1944. Source: British Army Staff (AFV) Situation Report Number 28 November 18th, 1944

March 1945 – All-Change, and the end of the T33

In March of 1945, everything changed for the T33 Cargo Carrier and T13 Armored Utility Vehicle. Cargo Carrier policy, as far as it affected the Armored Force and Tank Destroyer Command, appeared to the British to be focused around the T33 Cargo Carrier. The British at the time called the T33 an Armored Personnel Carrier. The discussion remained open as to if the overhead armored protection, previously mentioned back in November 1944, on the T13 was necessary as it was being contended at the time that its presence would prevent a complement of 30 men from leaving the vehicle speedily. On the other hand, it was also admitted that, with the development of the proximity fuse (VT Fuse), overhead cover was essential.
By the end of the month, the T33 Cargo Carrier was canceled in favor of the T42 Cargo Carrier/Prime Mover/Cargo Tractor. The T42 would be, at first, nearly identical to the T33 Cargo Carrier, but with the adoption of the M18’s 900-T Torquematic gearbox and the R-975-C4 radial engine as its powerplant. The T42 was also cross-adopted as a prime mover as Cargo Tractor T42 to replace the 18-ton High-Speed Tractor M4, a project that originally started in February of 1945.

The end of the T13

In April 1945, the T13 Armored Utility Vehicle, with the new powertrain adopted from the M18, was officially redesignated T16 Armored Utility Vehicle and the T13 Armored Utility Vehicle, based upon the chassis of the M24, canceled.
With the cancelation of the T33 Cargo Carrier and T13 Armored Utility Vehicle, work on another Cargo Carrier and Armored Utility Vehicle would continue on in the development of the T42(M8) Prime Mover/Cargo Tractor/Cargo Carrier and T16(M44) Armored Utility Vehicle both of which would become accepted into Standard and then Limited Standard service by the United States.

Sources

British Army Staff (AFV) Situation Report Number 25 August 18th 1944
British Army Staff (AFV) Situation Report Number 24 July 18th 1944
British Army Staff Royal Artillery Monthly Letters September 1944 Para 13 (012)
British Army Staff (AFV) Situation Report Number 27 October 18th 1944
British Army Staff (AFV) Situation Report Number 28 November 18th 1944
British Army Staff Royal Artillery Monthly Letters December 7th 1944
British Army Staff (AFV) Situation Report Number 31 February 18th 1945
British Army Staff (AFV) Situation Report Number 32 March 18th 1945
Technical Services Armaments Number 16 February 25th 1945
Technical Services Armaments Number 18 April 30th 1945
British Army Staff (AFV) Situation Report Number 33 April 18th 1945

Vehicle AUV proposal Cargo Carrier T33 AUV T13
Date August 1944 August 29th 1944 (reported on in October 1944) September 30th 1944 (reported on in November 1944)
Total weight 40,000 lbs (18,000 kg) 39,000 lbs (17,600 kg)
Empty eight 24,000 lbs (10,800 kg) 31,000 lbs (14,000 kg)
Crew 2 2 2 (likely)
Troops 9 0 16 (likely)
Total 11 2 18
Propulsion 2 Cadillac V8, 230 hp at 1400 rpms 2 Cadillac V8, 220 hp at 1400 rpms
Speed 34 mph (55 km/h) (Unsure) 35 mph (56 km/h) (Unsure)
Range 250 mi (400 km) 250 mi (400 km)
Armament M2 .50 cal machine-gun M2 .50 cal machine-gun
Elevation/depression +86 to -10 degrees +86 to -10 degrees
Fording ability 40 in (1 m) 40 in (1 m)
For information about abbreviations check the Lexical Index
Categories
WW2 American Prototypes

Pelican Project and Half-Track Amphibian Cargo Carrier T32

USA (1942-44) Amphibious Utility Vehicle – Scale model only

By July 1942, the US National Defense Research Committee (NDRC), while working on developing the DUKW amphibious transport, concluded that a larger amphibious vehicle would be needed. They presumably expected that the DUKW’s limited capacity of 2.3 tonnes would be inadequate during large scale landings. Testing was done on a number of converted trucks, however, it was found that wheeled vehicles with payloads over 6 tonnes faced severe problems due to the increased ground pressure and unsatisfactory traction on beaches, their most likely landing point. It was therefore decided that a new project would be started, looking at developing amphibious half-tracks. These were meant to provide forces with larger supply payloads during landings in Europe and the Pacific without the inherent problems that wheeled vehicles faced.

The GMC DUKW (“D” – year 1942, “U” – utility, “K” – all-wheel drive, “W” – twin rear axles), designed in 1941, started production at the end of 1942 and was to be the US Army’s backbone during naval landings. Source: warhistoryonline

The Pelican Project

As a result of converted trucks failing evaluation, a number of half-track designs were drawn up for the newly started Pelican Project. These ranged from payloads as little as 2 tonnes, all the way up to an ambitious 25 tonnes. Some designs, in an effort to lower ground pressure and increase traction even further, featured an extra set of front wheels. These extra wheels, if powered, could have increased off-road performance, but none of the designs with them were given any further consideration.
It is not known exactly how all these designs were judged, but the final design that came out of the project did at least see significant evaluation. As well as being the last design in the project, it was also one of the largest. Weighing an estimated 9 tonnes empty, with a 9-tonne maximum payload, the vehicle was to be 15.3 m long and 4.4 m wide, larger than any other amphibious vehicle at the time. The design was to use a Ford 400 hp V8 petrol engine powering a pair of either Kirsten-Boeing or Voith-Schneider vertical propellers, giving the vehicle a water speed of 13km/h.

Blueprint of the final design of the Pelican Project Source: Half-Track: A History of American Semi-Tracked Vehicles, by R. P. Hunnicutt
To take advantage of the large number of new M4 Sherman tanks being produced and to potentially ease the logistical burden of developing a brand new tracked vehicle, the Pelican half-track was to share its VVSS (Vertical Volute Spring Suspension) bogie design. It was to have two bogies per side, totaling four road wheels per side with a central separate return roller, as well as the same track link design as on M4.

VVSS suspension was the standard suspension design of most US armored vehicles until it was replaced on the M4 Sherman by HVSS (Horizontal Volute Spring Suspension). This surviving M4A4 can be found at the Portland D-Day Center, UK. Photo: Mark Nash
A full-width ramp at the rear of the vehicle provided access to the cargo hold which was large enough to accommodate a 6-ton 6×6 truck of any model. Unlike regular half-tracks, the 2.7m wide driver’s cab was placed at the very front of the vehicle in front of the engine. The driver was on the left and on his right would be seated the rest of the vehicle’s crew.
A number of scale models of the Pelican half-track were built and used in water tests, but the project was soon canceled and no working prototypes were built.

Half-Track Amphibian Cargo Carrier T32

In May 1944, the NDRC was requested by the Ordnance Department to once again design an amphibious half-track to assist during landing operations. One main difference with this new program, however, was that the vehicle was required to have a three quarter length track. This was similar to that of German half-tracks, instead of the much shorter two-bogie design of the earlier Pelican half-track and other US half-tracks. This design would reduce ground pressure by having significantly more track in contact with the ground and more road wheels to support to vehicle.
Sparkman & Steven, Inc., contracted by the OSRD (Office of Scientific Research and Development), drew up an initial half-track design with an empty weight of 17 tonnes, and a payload of 13.6 tonnes. At a maximum weight of 30.6 tonnes, this design greatly outweighed the earlier Pelican’s 18 total tonnes. This could be credited to the three quarter length track, but at 12.7 m in length and 3 m in width, the vehicle managed to stay significantly smaller in size.

Blueprint of the initial vehicle design. Note the sloped top edge of the hull, and the matching sloped waterline, suggesting the vehicle would be tilted back slightly when in the water. Source: Half-Track: A History of American Semi-Tracked Vehicles, by R. P. Hunnicutt
The vehicle was to be powered by the Continental R975-C4 petrol engine, coupled with the General Motors 900T Torqmatic Transmission. This combination, the same as on the M18 Hellcat, would have given the vehicle 400 hp with an estimated top speed of 48 km/h on land, and 13 km/h in water. The front two wheels were powered, and propulsion in water was provided by a pair of 711 mm (28 inch) diameter propellers underneath the rear of the cargo bed.


Scale model of the initial vehicle design. It is unclear why the model lacks the sloped top edge of the hull, the rounded bow, and the cover plate over the wheels that are present in the blueprint. It is possible these modifications were done in the time between the initial blueprint and the model being made. Source: Half-Track: A History of American Semi-Tracked Vehicles, by R. P. Hunnicutt
The tracks, being longer than those of the Pelican half-track, allowed the design to have 5 dual road wheels which were also substantially larger. The wheels were on independent torsion bars instead of VVSS bogies, giving them more vertical travel and providing a smoother ride. The tracks also differed from the earlier Pelican in that they were without return rollers, an unusual feature on US vehicles. The design of the links was the same as on the T87 105mm Howitzer Motor Carriage, an ongoing project to have an amphibious vehicle using M18 Hellcat components armed with a 105 mm howitzer, a project that ended soon after the war did.
The design was later modified to include an additional road wheel by moving the drive sprocket forward. The rear ramp was also reshaped to provide clearance when entering an LST (Landing Ship Tank), reducing its overall length to 11 m and its overall height to 3.05 m. On the 29th June 1944, the improved design was designated Half-Track Amphibian Cargo Carrier T32. It was requested that three prototypes be built for testing, but Army Service Forces denied the request and the entire project was canceled, just over one month after the project was started.

The revised design that was submitted for prototype testing designated T32. Source: Half-Track: A History of American Semi-Tracked Vehicles, by R. P. Hunnicutt


The ‘Pelican Project’ amphibious Half-Track.


Early version of the Half-Track Amphibian Cargo Carrier T32.


Later version of the T32.

These illustrations were produced by this article’s author, Mr. C. Ryan, and were funded by our Patreon Campaign.


Conclusion

While the Pelican design, had it been built, might have suffered to a degree because of its small ground contact area for its weight, both the Pelican and the T32 seem to have been reasonable designs for their requirements. Ultimately, the sheer number of DUKWs being produced from late-1942 onwards outmatched any potential production numbers of the two vehicles, making them largely redundant apart from their valuable ability to bring regular trucks and other large vehicles to shore.
The failure of both projects did not end the US’ interest in large amphibious cargo vehicles however, as they would go on to attempt others after the war. One such vehicle was the capable 7.3-tonne, 8-wheeled XM157 Drake in 1956, which did succeed at reaching the prototype stage. It failed to reach production, however, as the army’s interest became focused entirely on the far larger LARC-LX for its amphibious heavy cargo needs. A 4-wheeled vehicle with a 54-tonne payload, it would go on to serve in the Vietnam War and stay in service until 2001.
Dimensions (L-W-H)15.3 x 4.4 x 3.94 meters

Specifications (Pelican)

Total weight, battle-ready 9 tonnes approx.
Propulsion Ford 400 hp V8
Speed (water) 13 km/h

Dimensions (L-W-H)11 m – 12.7 x 3 x 3.05 – 3.34 meters

Specifications (T32)

Total weight, battle-ready 17 tonnes approx.
Propulsion Continental 400 hp R975-C4
Speed Est. 48km/h (land), 13km/h (water)
Payload 13.6 tonnes, several dozen passengers, or a single 6-ton 6×6 truck

Sources

R. P Hunnicutt, Half-Track: A History of American Semi-Tracked Vehicles, Presidio Press

Categories
WW2 American Prototypes

Williams Amphibious Vehicle

USA (1942) Amphibious Armored Vehicle – None Built

Nothing spurs invention like war they say, and this is very true for Allison Williams. On the 30th December 1942, Allison Williams, from Yazoo City, Mississippi, filed a patent for a design of one of the most unusual armored cars of World War Two.
The design was created with the intention of providing “amphibian vehicles of high maneuverability adapted to attack and destroy a military tank and provided with a plurality of independent self-contained power units for driving the same”
There are three elements therefore to the design. The amphibian nature of the vehicle, the anti-tank nature of the design and, finally, the drive system.

Robert ‘Bob’ Semple (21 October 1873 – 31 January 1955)Colonel Allison Ridley Williams (1891-1966). Photo: Nashvillekit via findagrave.com

The Designer

Colonel Allison Ridley Williams (1891-1966) was born in Benton, Mississippi on 10th August 1891. He did not limit himself to just this amphibian vehicle design. He was already known as an inventor specializing in electrical control systems in the 1930s with patents filed for various steering and braking system and was referenced in Popular Science Magazine in 1939 for an electrical device controlling braking when turning. During the war, he designed not only this vehicle, but also two more successful designs for mine clearance equipment in 1944. Post-war, he continued his electrical work with patents on electric brake control for vehicles and aircraft until 1960. He is referenced in most patents as living in Yazoo from 1930s until the late 1940s after which he moved to Vicksburg, Mississippi, where he died on 27th August 1966, aged 75.

Nature and Design

The first two elements of this design are connected. Williams was clear that whilst military tanks were well designed using caterpillar tracks, too much reliance had been placed on defeating them with tanks. As those tanks have roughly the same limitations imposed on them by using caterpillar tracks and extreme weight, the solution was to go light and to go mobile. As most tanks are unable to operate in water, an agile vehicle able to operate both on- and off-road and also just as capably in water would allow it to flank enemy tanks. Add in an anti-tank gun on such a platform and suddenly you have an extremely capable tank destroyer which can go where tanks cannot.

Rear view of the amphibian vehicle providing a good view of the tyre tread and overall height of the vehicle. Source: US Patent US2432107
Given that the design was drawn up in 1942, after the USA had started fighting the Japanese in the Far East, the abundance of soft, marshy or marginal ground etc. would have made the deployment of such a machine very desirable. An obvious additional advantage is that the vehicle would not be reliant on landing craft or bridging equipment to cross rivers or lakes.

Armor

No specific armor is specified, but Williams is clear that the crew must be protected from enemy gunfire and that the drive mechanisms, in particular, should be well armored. With the body armored it makes sense to armor the wheels too, as this has the advantage of lowering the center of gravity for the design, an important consideration when floating or traversing rough country. Steel was the material of choice for the machine, specifically ‘heavy steel shells’ for the wheels, which, with the combination of the angled surface and thickness, ensured that no bullets or small caliber shot were going to incapacitate the vehicle. Puncturing of the wheels would be especially hazardous if the vehicle was floating, although the air pressure inside the wheel cavity was to be maintained at a pressure higher than the atmospheric pressure outside to resist the entry of any water. As the vehicle would float at half the height of the tires, a large amount of the vehicle would still be exposed to fire when crossing water.

Armament

Although the caliber of the main armament is not given, Williams is clear that a single anti-tank gun should be carried and although he doesn’t specify which sort of standard anti-tank gun in military service was likely envisaged. Additionally, a plurality of other armaments could also be carried in addition to, or instead of, this anti-tank gun. This armament is carried within a large fully rotating turret atop the main body of the vehicle, with rotation driven from below via a system of gearing. The turret provides for an elevation range on the main gun of -10 to +15 degrees. The turret itself is very tall, more than half of the height of the overall vehicle, and connects to the very low flat hull. As such, the hull provides a very small target from both front and side. Inside the turret, the main gun is mounted not on trunnions, as in a conventional turret, but on a turret floor mounted pintle allowing for completely independent slewing of the gun, which is partly independent of turret rotation. In this manner, the gun could be moved 30 degrees (15 degrees left and right). A smaller gun coaxial to the main gun is also drawn and presumably was a machine-gun.

Top-down view of the Amphibian vehicle showing the ability of the anti-tank gun to slew independent of the turret. Source: US Patent US2432107


A four-view illustration of Williams’ Amphibious Vehicle produced by ‘Giganaut’, funded by our Patreon Campaign.


Crew

The crew selected was to consist of four men. A commander, a driver, gunner, and the fourth member who was to act as a lookout or replacement gunner or driver. Presumably, if the machine to see action, he would simply have been a loader for the main gun. All of these crewmen were to be enclosed within the turret as there is no space within the hull for them and no indication of any access hatches for them in the hull. All access to the vehicle is provided for by means of a single large hatch on the top of the turret. Historically, crew-in-turret designs have failed due to the inability to move the turret whilst driving as it disorientates the driver, but, as the gun can slew independent of the turret, the design at least permits some offensive action to be taken without any turret movement distracting the driver.

Spherical wheel with drive unit contained inside. Source: Patent US2432107.

Power

Unlike a conventional armored car, the William Amphibian Vehicle had not just one engine and a transmission, but no less than four completely separate and independent power units protected by “good armor” within a watertight spherical wheel. Each power unit was enclosed within the completely spherical wheels covered, as in the patent drawing, with a tread pattern for both grip off-road, and for drive in water. Each wheel was mounted on a pivoting bracket permitting the wheel to move horizontally but not vertically. A hydraulic coupling moved through this pivot connection running to the engine for the machine. Therefore, a single engine located in the body of the wheel drove it with the speed of the motor determined via a hydraulic linkage permitting both flexibility and protection from shock. Whilst this system was very complex it had significant advantages for the design providing a lower center of gravity, reducing hull size and weight and improving the balance in the water.
Driving and steering were done by means of a joystick controlling the delivery of pressurized fluid via the couplings to each drive. More pressure to the left drove the left-hand wheels harder than the right causing a right turn and vice versa. Thus, steering of the vehicle was remarkably simple, especially compared to the steering levers common to tanks of the era. Acceleration, therefore, would be by means of uniform forwards pressure on the stick and slowing down by the stick being pulled back. Presumably, this stick would be spring controlled so that its natural position was in the ‘back’ position with no pressure applied to any motor. Should any one motor fail, the vehicle could still maneuver, and as long as at least one motor was still functional on each side, the only effect of losing the other two power units would be reduced performance. Engine exhaust did not, as might be expected, vent out through the outside of the wheel, but actually backward through the inside of the coupling through a one-way valve. Air for the engine was supplied through the same linkage as the hydraulic coupling and links back through the crew compartment to the roof. Each motor sucked in external cool air through the crew area providing relief from heat and fumes for the crew.

Manufacture

Each wheel was to be made from two hemispherical shells bolted together around a central rubber tired wheel acting as a normal wheel when on a paved road. As the ground got softer then progressively more of the wheel would be in contact with the ground. In this way, the wheels actually gained significantly more traction even when sinking very slightly and even when the ground became unable to bear the weight of the vehicle would actually be buoyant.

Conclusion

The Williams Amphibious Vehicle is an unusual vehicle in many regards. The selection of having all the crew in the turret is not unique but it also is not common either. The drive system is probably the most unusual part of the design and although hub-motors have been around a long time offering lots of potential benefits the military, in general, prefer simpler and cheaper conventional drive systems. Whilst the Williams Amphibious Vehicle looks odd with its ball-shaped wheels and tiny body the design is undoubtedly sound, at least on paper. In many ways given the nature of fighting the US had to do between 1943 and 1945 a vehicle with the sort of mobility Williams envisaged could have proven to be very useful but as it was the design was not developed. Perhaps an opportunity missed.

Source

US Patent US2432107 filed 30th December 1942, granted 9th December 1947
Popular Science Magazine July 1939
Yazoo Herald, Mississippi 20th April 1961
Findagrave.com

Categories
WW2 American Prototypes

Wrona Tank

USA (1940-43)
Tank/APC – Blueprints Only

Frank Stanley Wrona of Aurora, Illinois, had his go at supporting the war effort in World War Two even before the United States had declared war. On the 18th September 1940, just over a year after the German invasion of Poland started World War Two, Frank Wrona applied for a patent on his own design for a ‘Military Tank’.

Purpose and Design

The design was very specific in its intention. It was shaped with its pointed nose and curving body to maximize the chances of deflecting bullets and shrapnel and provided with ventilation to remove fumes and heat from inside whilst still protecting the crew from noxious gas and flamethrowers.
The overall shape is best described as an uncut cigar, pointed at the front and rounded at the back. On each side are two rectangular shuttered loopholes and two large rectangular doors. In the front are two roughly square-shaped openings for the main guns, and in the roof, are ten vents opened by means of a rod and handle-crank system. The whole system is meant to be carried on a rectangularly shaped hull between two sets of tracks, each with six wheels.

Side view and top sections of the Wrona Tank design intended to show the positions of the multiple roof vents. Image: US Patent US2319178
The outward opening doors for access and exit were to be provided in opposite sides of the vehicle and fitted with an internal locking mechanism by means of a turned nut to lock them into place. When opened, they moved upwards like a clamshell door, although there is no spring or power system to assist in the opening of what would be a very heavy armored door. The six wheels are crudely drawn on what appears to be a very rigid type of suspension which is not described. No system of propulsion is described either, although presumably, he envisaged this would go below the floor level of the main compartment in the rectangular box-shaped section between the tracks.

Armor

The walls of this cigar shaped tank are simply described as “heavy armor plates suitably welded or otherwise secured together” fabricated by means of attaching them to a rigid frame. No thicknesses is mentioned, but to be bulletproof, it is reasonable to expect 10mm or so, which, considering the size of the area being protected, would still have resulted in a very heavy vehicle.

Front and sectional view of the Wrona Tank showing the cigar-shaped body sitting atop a rectangular box attached to the tracks. The dotted portion represents the side door in the open position. Image: US Patent US2319178


Illustration of the Wrona Tank in a fictional livery based on period examples. It was modeled by Mr. C. Ryan, funded by our Patreon Campaign.

Firepower

Multiple large caliber guns in sealed compartments are arranged along the front, and smaller caliber guns “such as machine-guns” would be fireable from inside hidden shutters along the sides of the tank as required and which would slide to the side to expose the guns, fire, and then slide shut under spring pressure. At the front are two guns “preferably… of an extremely large caliber be mounted in the front end with the barrels, therefore, protruding through openings provided in the body”.

A sectional view of the Wrona Tank showing the very naive arrangement of firepower within the huge crew space. Image: US Patent US2319178
The two main guns pointing forwards appear to lack the ability to move inwards meaning there would be a blind spot directly to the front of the tank and the positions would have very limited traverse of just 10 degrees or so to the outside. This is a very poor arrangement for the main firepower of the tank preventing both guns being trained on a single target at the same time and meaning the entire vehicle has to turn to slew the guns properly. The side guns are poorly situated too. Sat on fixed pedestal mounts and firing through narrow openings covered with shutters they lack the ability to even provide overlapping fire. Considering the number and weight of weapons selected for the design, this is a large oversight. The machine-guns are described but not drawn, and it is possible that the designer simply envisaged these machine-guns as being the means to cover these gaps, but it is not described how this would be done.

Conclusion

It is, frankly, a terrible design. It would not have been a good design for World War One let alone World War Two. The idea that, between all of those shuttered openings, doors, and roof vents it could remain immune against chemical attack or flamethrowers is simply not realistic. The number and position of the firepower are totally unsuitable with no rationale presented as to why it would need the number and type of guns mentioned. The armor, at just ‘bulletproof’, is woefully unsuitable for such a large and inevitably heavy tank and the shape itself would cause problems. It would be far too large to easily transport and with the size of the overhang at the front probably would just become stuck in rough country. The tank then exemplifies many of the problems of amateur design not thinking through the problems and compromises inherent in the design of a vehicle as complicated as a tank and no doubt these obvious limitations were amongst the reasons the design never left the pages filed at the Patent Office.
Frank Wrona clearly thought the design had some merit though, as he also submitted it to the Canadians for their consideration and was granted a patent by the Government of Canada in February 1942. As far as can be ascertained, this was as far as Mr. Wrona’s military inventiveness went and no other patents are filed in his name for tanks or anything else.

Sources

Canadian Patent CA402879 granted 17th February 1942
US Patent US2319178 filed 18th September 1940, granted 11th May 1943

Categories
WW2 American Prototypes

APG’s ‘Improved M4’

USA (1941)
Medium Tank – Blueprints Only

Developed to meet the needs of both the American and British military during the Second World War, the Medium Tank M4 became one of the most produced tanks in the world. It was reliable, versatile and spawned a number of variants through the course of its production.
However, before the first vehicles were rolling off the assembly line, plans were hatched to improve on its design…

An original concept for an improved M4. Photo: Presidio Press

The M4

The tank started life in 1941 as the T6 and was later serialized as the Medium Tank M4. There were two initial models namely the M4, which had a welded hull, and the M4A1, which had a cast hull. The tank entered service in 1942.
The M4 was armed with the 75mm Tank Gun M3. This gun had a longer barrel length (compared to the previous M2 model) which allowed a muzzle velocity of up to 619 m/s (2,031 ft/s) and could punch through 102 mm of armor, depending on the AP (Armor Piercing) shell used. It was a good anti-armor weapon, but it was also used to great effect firing HE (High-Explosive) for infantry support. For secondary armament, the M4 had a coaxial and a bow mounted .30 Cal (7.62 mm) Browning M1919 machine gun, as well as a .50 Cal (12.7 mm) Browning M2 heavy machine gun on a roof-mounted pintle.
It was well armored for its time, with 50.8 mm (2 in) of frontal hull armor angled at 55 degrees which brought the effective thickness to 88.9 mm (3.5 in). The front of the turret was 76.2 mm (3 in) thick.
Propulsion was provided by a Continental radial gasoline engine, developing 350-400 hp. A drive shaft sent the power from the engine in the rear of the tank to the transmission at the front. This powered the drive wheels and propelled the vehicle to a top speed of 22–30 mph (35–48 km/h). The tank’s weight was supported on a Vertical Volute Spring Suspension (VVSS), with three bogies on each side of the vehicle and two wheels per bogie. The idler wheel was at the rear.

Aberdeen’s Improvement Project

Before the M4 had even entered production, Aberdeen Proving Ground (APG) received a letter from the Office of the Chief of Ordnance, dated December 8th, 1941 (the day after the Pearl Harbor attack). The letter instructed Aberdeen to start work on developing an improved model with increased mobility and protection. Two designs were submitted. These were Aberdeen Proving Ground’s own and another submitted by Detroit Arsenal. Aberdeen submitted line-drawings and a list of characteristics of their initial design on March 13th, 1942. The proposed vehicle had a number of differences from the first models of M4. It did, however, retain the 75mm M3 tank gun and M34 mantlet, as well as the coaxial and bow mounted .30 cal (7.62mm) machine guns.

A head-on view of the design, also showing the thicker tracks. Photo: Presidio Press

Hull

The front hull armor thickness of 50.8mm (2 inches) remained unchanged, except for the bulbous final drive housing. At the time of this design, the final drive housing on M4s was made up of three parts bolted together. This new design did away with that, making it one solid piece. Such housings would later appear on subsequent M4 production models. The vertical portion of the housing, originally 2 inches thick, was increased to 3 inches (76.2mm) and the contour increased to improve effectiveness.
The lower side armor (behind the tracks) was also increased from 1.5 inches (38.1mm) to 2.5 inches (63.5 mm). Above the track, on the sponsons, armor was increased from 1.5 inches to 2.75 inches (69.85 mm). The plate was sloped inwards at 30 degrees from the vertical which increased the width the entire hull to 123 inches (10.5 ft) from the original 103 (8.5 ft). The rear plate was also thickened from 1.5 inches (38.1 mm) to 2 inches (50.8 mm).
When this design was presented, it was thought that there would be a large shortage of foundry capacity to produce large castings such as those for the M4’s turret. As such, it was decided to fashion the turret from a number of rolled armor plates welded together. This would give a sharp, angular silhouette to the turret.

A top down view of the design showing the angular shape of the turret. Photo: Presidio Press


Representation of APG’s ‘Improved M4’ in a speculative Olive Drab colour scheme that was common at the time of its conception. Illustration by Bernard ‘Escodrion” Baker, funded by our Patreon Campain.

Mobility

It was thought that the original Continental engine would be too underpowered for this new design due to the weight increase from approximately 30.5 tons to 42 tons in view of to the additional armor. Aberdeen proposed the use of the new Wright G200 air-cooled radial engine which would develop 640 hp, compared to the previous 400hp. A large bulge had to be drawn into the engine deck to accommodate the engine. The standard transmission used in the M4 was retained, but the drive shaft from the engine was mounted lower in order to increase room inside the tank. It was expected that this new power pack would propel the tank to about 35 mph (56 km/h) which was a substantial improvement over the 22-30 mph (35-48 km/h) top speed of the standard M4.
The weight increase also necessitated changes to the tracks and suspension to support the heavier hull and keep ground pressure to an acceptable limit. Aberdeen chose to use a slightly modified version of the suspension found on the Heavy Tank M6 and the prototype Heavy/Assault Tank T14. This was an early version of a Horizontal Volute Spring Suspension (HVSS). Three bogies were mounted per side, each with two double-wheels. The wheels were 18-inches (45.72 cm) in diameter, apart from the first wheels on the front bogie, and the trailing wheel on the rear bogie. These wheels were larger with a 22-inch (55.88 cm) diameter. The bogies did not have integrated return rollers like the traditional M4 suspension. On this design, there were four mounted directly to the side of the lower hull on each side. The M6/T14’s 25.75 inches (65.40 cm) tracks were also chosen for the tank. Aberdeen surmised that the new vehicle would have a combat weight of approximately 42-tons. Almost 12 tons heavier than the standard M4.

This side profile of the design shows the intended HVSS suspension. Photo: Presidio Press

Detroit Arsenal

The Aberdeen design was not approved for production as there were additional areas that needed further development. Detroit Arsenal continued looking into the possibility of upgrading the M4. They looked into both welded and cast turrets for their design. This turret would have interchangeable front plates enabling it to either carry the 75mm M3 Tank Gun or the 105mm M4 Howitzer or even the M7 3” Gun from the GMC M10 “Wolverine”.
Detroit kept the vehicle’s weight to 30.5 tons, around the same as the standard M4. Armor effectiveness would be increased however in a manner similar to the T14. The hull was made considerably more shallow and the raised ‘hoods’ over the driver’s positions eliminated. This turned the upper plate a perfectly flat, sloped surface. The sponson armor retained the standard thickness of 1.5 inches (38.1mm), but was sloped inward at 30-degrees. This increased the vehicle width to 120 inches (10 ft). As the armor was not increased, the weight of the tank did not climb. As such, it was planned that the standard M4 VVSS suspension would be retained. Three engines were considered for installation on the tank. These were the Ford GAZ, Continental R975-C1, and the General Motors 6046 diesel.

The Detroit Arsenal design. Photo: Presidio Press

Conclusion

The design programs had succeeded in finding numerous potential improvements for the M4 tank, but there were some design choices that were not such an improvement.
Ammunition for the main armament was still intended to be stored in the sponsons. Although this was the perfect place for the loader to access his rounds, it was an extremely vulnerable position. The fuel tanks were relocated from the engine compartment to underneath the turret basket. One can only imagine the catastrophic events that may have occurred should the fuel tanks have been breached and set ablaze.
Though neither the Aberdeen or Detroit vehicles were approved for service, however, the work put into the developments were not in vain, as subsequent models of the M4 would incorporate some of the improvements identified in these projects.

An article by Mark Nash

Specifications

Total weight, battle ready 42 tons
Crew 5 (commander, driver, co-driver, gunner and loader)
Propulsion 640hp Wright G200 air-cooled radial engine
Speed (road) 35 mph (56 km/h)
Armament 75 mm M3 Gun,
.50 caliber MG HB M2 flexible AA mount on turret
.30 caliber MG M1919A4 coaxial w/75mm gun in turret
.30 caliber MG M1919A4 in bow mount
Armor 1.5 inches (38.1 mm) – 3 inches (76.2 mm) – 107.95mm

Links, Resources & Further Reading

Presidio Press, Sherman: A History of the American Medium Tank, R. P. Hunnicutt.

Categories
WW2 American Prototypes

Flame Thrower Tank T33

USA (1945)
Mechanized Flame Thrower – 3 Prototypes

With M4-based mechanized flamethrowers proving highly effective against the heavily dug-in Japanese in the Pacific, development of newer versions moved quickly. In 1945, a number of experiments took place to test the possibility of mounting a powerful flamethrower coaxially with the main gun. a progression of this was designated by the United States Ordnance Committee as ‘Mechanized Flame Thrower T33
Considered by some to be “the ultimate US flamethrower of World War Two”, the T33 saw one of the more extensive modifications to its foundation M4 hull. It featured a new turret, a new cannon, and a new flame gun.

The T33 prototype at the Aberdeen Proving Grounds. Photo: Osprey Publishing

Turret

To accommodate the tank’s main gun and new coaxial flame gun, a new turret had to be designed for the T33. It was of cast construction and rather bulbous and large compared to most M4 mounted turrets. The main gun remained in the center of the turret, with the flame gun placed on the right. The projector was protected by a thick tube, which almost gives it the appearance of a short-barreled howitzer.
It was a three-man turret. The commander sat in the center at the rear, the loader was positioned on the right and the gunner on the left. This was an unusual arrangement for an American tank, as usual, crew orientation concerning the loader and gunner are the opposite way around. Above the commander was his vision cupola with built-in hatch. The gunner and loader had individual hatches above their positions.

Weaponry

The flame gun and cannon were geared together, but could also move independently of each other in elevation. The range of elevation was -15 to +45 degrees. It also had 15 degrees of traverse left and right. The particular flamethrower used in the T33 was the E20-20 (E20 fuel group combined with the E20 flame gun) which was a further development of the POA-CWS-H5 (Pacific Ocean Area-Chemical Weapons Service). This weapon was also designed in 1945 and was earmarked for use in the planned Invasion of Japan. The weapon had a range of 150 yards (137 meters).
For a long time, the standard gun of many M4 models was the 75mm Tank Gun M3. To save weight and grant extra space in the new turret, in the T33 this gun was replaced with the 75mm Lightweight Tank Gun M6 which had a concentric recoil system (a hollow tube around the barrel. A space-saving alternative to traditional recoil cylinders). This gun also served as the main armament of the Light Tank M24 Chaffee. Variants of the gun were also used on aircraft such as the B-25H Mitchell Bomber. Though one caliber shorter than the M3 (The M3 Tank Gun was 40-Calibers in length, the M6 was 39), the gun granted the same velocity of 619 m/s (2,031 ft/s) and identical maximum penetration of 109mm. Elevation range of the gun was -10 to +13 degrees. The gun also had a coaxial.30 Cal (7.62mm) Browning Machine Gun which was mounted in between the canon and flame gun. Between 40 and 55 rounds of 75mm ammunition were carried.
It was planned that, when available, the M6 gun would be replaced by a new model designated the M17. This gun was similar to the M6, but saw the introduction of a muzzle brake. The replacement would never take place, however, as no M17s would enter production.

Schematics of the layout of the flamethrower equipment inside the T33. Photo: Presidio Press
Originally, there was a specification to add an Auxiliary E21 Flame Gun to amount installed on the commander’s cupola. It could traverse 240 degrees left and right, providing close range protection from attacking infantry. It was blocked firing directly forward to avoid flaming liquid pooling on the turret roof. When the T33 pilot was constructed, the E21 was replaced with the E12R4. This was also a small auxiliary flamethrower. Two large fuel tanks were placed on the hull floor, with two smaller ones located on the left and right of the turret bustle. Total fuel capacity for the flame guns was 250 US Gallons (1137 liters).
To begin with, the tank also retained the original M4 crew of 5 (commander, gunner, and loader in the turret, with the driver and co-driver/bow gunner in the forward hull. This soon dropped to four men, however, when the bow machine gun was removed. The void was welded over.


Artist’s interpretation of the T33. As there are no known schematics, or any clear side photos, the illustrator has speculated on the details and shape of this side of the turret. Illustration by Andrei ‘Octo10’ Kirushkin, funded by our Patreon campaign.

Production

A pre-production run of 20 T33s was planned, with 300 requested for January 1946. There were further aims to construct 600 of the tanks. However, when the war with Japan ended, this was drastically cut back to just three pilots. The particular hull chosen for the T33 pilots was that of the Assault Tank M4A3E2, the famous Sherman ‘Jumbo’.
The E2 was famous for having much thicker armor than its standard M4 brothers. At maximum, the armor was 177 mm (7”) thick. The effect of which was amplified by the flat, sloped upper plate. It is interesting to note that the E2s chosen for the project were three of the only four to remain in the United States as all others were sent overseas.

A front view of the T33. Presidio Press
The standard Vertical Volute Spring Suspension (VVSS) of the E2 was replaced with the newer Horizontal Volute Spring Suspension (HVSS). This suspension had two-part wheels and used a wider track. For a heavy vehicle, which the Jumbo was, a wider track granted better weight-dispersion on soft ground making it easier to traverse.
Although the original Ford GAA V8 power plant from the standard M4A3 was retained, the final drive ratio was increased to 3.36:1. This reduced the top speed to 22 mph (35 km/h), but the tank maintained reasonable acceleration even though it now weighed 84,000 lbs (38,100 kg). It could climb a 60% slope, cross a 7’6” (2286 mm) trench, climb a 24” (609 mm) vertical wall and ford 36” (914 mm) of water.

A rear view of the T33, showing clearly the the HVSS suspension. Photo: Presidio Press

Fate

At the end of the war, the T33 was considered the most advanced flamethrower tank in existence. Although slow, work continued on these pilots after the war. The Pilot #1 arrived at Aberdeen in September 1947, Pilots #2 and 3 arrived in January 1948. The T33s took part in tests at Aberdeen, but no further production would take place.
Though the T33 did not enter service, the E20-20 and coaxial configuration did. Mounted coaxially with the 105mm Howitzer armed M4A3 (HVSS), it served during the Korean War.
In 1953, two of the T33 pilots were converted into the Self-Propelled Flame Thrower T68. This was based on the Canadian Badger project. The turrets of the T33s were removed and the void covered by sheet metal with a cupola added on top. Attached to this cupola was a mount for a .50 Cal (12.7mm) machine gun. A 220 US Gallon fuel tank fed a flamethrower gun mounted in the bow machine gun position. The tank had a crew of three, consisting of driver, commander, and flame gun operator. The T68 took part in a number of tests at Aberdeen but, like the T33, it never entered production.

An article by Mark Nash

Specifications

Total weight, battle ready 38 tonnes aprx.
Crew 5 (commander, driver, co-driver, gunner and loader)
Propulsion Ford GAA V8, 500 hp@2600 rpm
Speed (road) 35 mph (56 km/h)
Armament E20-20 (E20 fuel group combined with the E20 flame gun)
75mm Lightweight Tank Gun M6
Armor Maximum 177 mm (7”)

Links, Resources & Further Reading

Presidio Press, Sherman: A History of the American Medium Tank, R. P. Hunnicutt.
Osprey Publishing, New Vanguard #206: US Flamethrower Tanks of World War II
US Army Ordnance Department report, dated 31st May 1945

Categories
Failed Tanks WW2 American Prototypes

E9-9 Mechanized Flame Thrower

U.S.A. (1943)
Flamethrower Tank – 1 Prototype

In 1943, the Standard Oil Company, based in Indiana, was one of the main companies charged with designing tank-based, or ‘Mechanized’ flamethrowers. Earlier in the year, in January, they had successfully tested their E7-7 model. This was a modified Light Tank M5A1 with the 37mm gun exchanged for a flame projector.

In April, Standard Oil was contracted to develop another tank based flamethrower. This time it would take the ‘Auxiliary’ form. Simply, this means that the flamethrower is secondary to the main gun, and does not replace it. This is unlike the ‘Main Armament’ flamethrowers, such as the M3A1 Satan or E7-7’s, which replaced the main gun.

This new flame thrower would be designated the E9-9 (this was the combination of the E9 Fuel system and E9 flame gun). The vehicle would follow the same designation, being called the E9-9 Mechanized Flame Thrower. It is sometimes known as the ‘Indiana-Merz E9’, though what ‘Merz’ relates to is unknown.

The E9-9 Mechanized Flame Thrower. Photo: Presidio Press

The M5A1

The M5 was the last in the lineage of light tanks which had followed the same design since the Combat Car M1 which entered service in 1935. Entering service in 1942, the M5 was designed to replace the now aging M3. It was originally going to be designated the M4, but to avoid confusion with the Medium Tank it was changed to M5.

Overall the design was similar. It shared the same vertical volute spring suspension (VVSS) and 37mm gun main armament. The real differences lay with the hull design and engine. The hull was a completely different design but followed elements used on the M3A3. Gone was the stepped armor layout at the front of the tank. It was replaced by a large sloped plate, granting more effective protection.

The original twin Cadillac Series 42 engine was replaced by another Cadillac model. This time twin V-8 automobile engines were used. The M5 gradually replaced the M3 in active service. After the fruitless M7 project, the M5 was replaced with the M24 Chaffee, a completely new design.

A Stuart Crocodile?

The aim of the E9 program was to produce a tank-based flame thrower with a large fuel capacity, a projection range of 200 yards (183 metres) and that would not reduce the M5A1’s original firepower. To achieve this, all the flame thrower equipment, such as the fuel tanks and propellent gas bottles, were placed in a trailer that was towed by the tank. The only part of the system installed on the tank itself was the flame projector, mounted on the front of the tank. This configuration is similar to the famous Churchill Crocodile and lesser-known Sherman Crocodile. Both of these flame throwing tanks kept all of their fuel and gas load in a towed, wheeled trailer.

By comparison with the trailers of its Crocodilian cousins, the E9’s was extremely large. It was approximately the same height and width as the tank itself. In this 12 ton trailer, there was a 1200 US gallon (5455 litre) armored steel tank. This would be filled with 800 US gallons (3637 litres) of flame fuel. The 400 US gallon (1818 litre) void that was left was employed as an air cushion. There were two air-compressors in the trailer which provided 800 psi from a bottle above the fuel tank.

The trailer was attached to the rear of the M5 via a 10-inch (254mm) diameter ball-and-socket joint. The joint granted the trailer the ability to turn 105-degrees left or right from the center line. The fuel line which fed the projector passed through this ball joint. In an emergency, the trailer could be jettisoned. Valves in the piping would close upon this action to prevent fuel from the tank spilling.

Another view of the E9 with 2 two crew members, showing the size of its large trailer. Photo: Osprey Publishing

The E9 Flame Gun

The flame projector was mounted in between the drive sprockets at the front of the tank. It was operated by the bow machine gunner/assistant driver through a series of pulleys and cables. The flame gun could traverse 60-degrees left and right, and elevate +30 to -15 degrees.

The E9 was a duplex flame gun, meaning it had two nozzles side by side. One nozzle was ¼ inch (6.35 mm) in diameter, the other was ¾ inches (19.05mm) in diameter. The thinner nozzle was tighter, this granted a higher pressure thus providing greater range. The wider nozzle did the opposite and provided a wider field of fire at closer ranges.

A diagram of the flame gun and puly system. Photo: Presidio Press.

Catastrophic Tests

The E9-9 project would come to a deadly end, meaning tests would never be completed. During a live fire trial on the 29th of May 1944, 500 US gallons (2273 liters) of Napalm thickened gasoline was provided and prepared in the trailer’s fuel tank. The tank was pressurized to 500 psi. During a fire test, one of the air compressors failed. Shortly after this, the main fuel tank exploded ripping the trailer apart and engulfing the M5 in flames. The incident was fatal, resulting in the death of all four tank crew. This catastrophe brought about an abrupt end to the E9-9 project, with all work halting. As a result, none of the E9 equipment survives today.



Illustration of the E9-9 without fuel trailer by Tank Encyclopedia’s own David Bocquelet

M3 Stuart specifications

Dimensions 4.62 x 2.39 x 2.33 m (15’2″ x 7’10” x 7’8″)
Total weight, battle ready 16.5 tons (tank) + 12 ton trailer (28.5 tons)
Crew 4
Propulsion Twin Cadillac V8, 296 hp (220 kW), air cooled gasoline
Speed 58 km/h (36 mph) road
29 km/h (18 mph) off-road
Range 120 km at medium speed (74.5 mi)
Armament E9 Flame thrower gun
37mm Tank Gun M6
1x Browning .30 Cal. (7.62 mm) M1919 machine gun
Armor From 13 to 51 mm (0.52-2 in)

Sources

Presidio Press, Stuart – A History of the American Light Tank Vol. 1, R.P. Hunnicutt
Osprey Publishing, New Vanguard #186: US Marine Corps Tanks of World War II
Osprey Publishing, New Vanguard #206: US Flamethrower Tanks of World War II
Fort Leonard Wood, U.S. Army Flame Thrower Vehicles, Part 1, Captain John Ringquist


Categories
WW2 American Prototypes

AGF Improved Medium Tank

U.S.A. (1944)
Medium Tank – None Built

The period starting at the end of the Second World War and going into the new postwar world was a very busy time for US tank design despite the slashing of many programs and budgets from March 1945 onward. The scale of US experiments makes it hard to separate out one design from another as there was so much overlap between armor requirements, speed, and firepower. There was also the switch in the perceived enemy, no longer were tanks being conceptualized to fight the Germans or even the Japanese but instead to fight the armor of the Soviet Union. The enormous number of ideas, concepts, and proposals is simply overwhelming but one project stands out as an example of one of the less extreme ideas.
The ‘Improved Medium Tank’ may date back as far as September 1944 according to ‘Faint Praise’ by Charles Baily. This is based on the date given for the artist’s impression which is the only known image of what this vehicle would look like and which is used into 1945 for the project. The paperwork relating to the design is a little later though and the whole concept stems from the need to develop a new medium tank to replace the older obsolete M4 series. The replacement for the M4 was not a straightforward process though and the Army Ground Force (AGF) had failed to get the T25 Medium Tank into production and they weren’t satisfied with the suggestion from the Ordnance Department for the T20 series tank either. This meant that they did not have a replacement medium tank in development for the army (the T26 was still classed as a ‘heavy tank’ at this time). Clearly, this was an unacceptable situation and the result of this medium tank deficiency was that the AGF simply created their own requirement for a new medium tank instead. This new medium tank can, therefore, be called ‘The AGF Medium Tank’ and a look at the requirements gives a good impression that the AGF really had paid a lot of attention to the needs of combat and of tank crews. They also seem to have allowed some unrealistic expectations to creep into their thought process too as will be apparent in a review of the statistics for the vehicle.

Improved Medium Tank from artists impression 28th September 1944.
The AGF submitted the specification for their 45 ton medium tank on the 6th of December 1944. It was almost immediately rejected on the basis that the specifications were expected to result in a tank of 60 tons because of  “increased bulk requirements due to the demand for increased power, cruising range and larger diameter turret ring…” and was even called “amateurish” but it could not simply be dismissed without some kind of study being conducted. The Ordnance Department, busy with their own program, would not conduct a study of a rival product.
It was on the 2nd January 1945 that the Army Ground Force met in Washington D.C. to finalise their ideas. Their report was ready on the 20th June 1945, just after the war in Europe had ended. Among other vehicles, the report specified that the new medium tank had to be in the 45 ton class. Exactly what the differences between this concept and the initial one are is not entirely clear but some hints can be gleaned from the specifications.
The purpose of the AGF 45 ton Improved Medium Tank was simple; it was to be the “primary weapon for tank units, both in armored divisions and separate tank battalions”. The specified fully laden combat weight of this tank was listed as 90,000lbs, which is 40,823kg, just over 40 metric tonnes or 45 US short tons. No dimensions are listed explicitly except width which was to be at most 134 inches (3.4 metres) due to transport requirements with height and width only to be the “minimum consistent with efficient construction and design”.
Protection was to be from rolled homogenous armor and “all armor should be as heavy as possible consistent with weight limitations, any reduction in armor thickness should be proportional” with a minimum of 6″ (152.4mm) for the hull front although 8″ (203.2mm) was desired. Just to illustrate, the minimum requirement was the same thickness as that of the frontal glacis of the Königstiger! The hull sides were to be 3″ (76.2mm) thick on the sponsons around the crew compartment, down to just 1.5″ (38.1mm) thick over the engine and the lower half of the hull sides over the crew compartment was to be just 2″ (50.8mm) thick. The hull rear was also to be 1.5″ (38.1mm) thick, with a 1″ (25.4mm) thick floor under the crew compartment and just ½” (12.7mm) thick under the engine. The hull roof was to be 2″ (50.8mm) thick over the crew compartment down to ¾” (19mm) thick over the rear of the hull.
The turret, which was to have a turret ring with a diameter of at most 80″ (2032mm), was to match the frontal protection with 6″ (or preferably 8”) of armor including the mantlet, 3″ (76.2mm) thick at the sides, 2.5″ (63.5mm) thick at the rear and a 1″ (25.4mm) thick roof.

Armament

Surprisingly for a future medium tank, this vehicle was selected to have a main gun of not more than 3″ (76.2mm) caliber stating that the gun must be “specifically designed in view of the space limitation in tanks.” Specific requirements for the gun were that it was to have the smallest possible chamber size, a compact recoil system with a short recoil stroke, and the shortest possible distance from the trunnion to the semi-automatic breech block as possible.
The single piece ammunition for the gun was to achieve the specified performance of being able to defeat enemy armor up to 8″ (203.2mm) thick at an angle of 30 degrees at a range of 1000 yards (915 m). The firing though would have to cause as little smoke as possible as there was a problem with target obscuration after firing and it had to not cause excessive barrel wear. The dimensions for the ammunition were specified to not exceed 35 lbs in weight (15.9kg) or be longer than 30″ (762mm) inches in length with a total length of 33″ (832.8mm) being the absolute limit.
The penetration requirement of just over 200mm was certainly not impossible with the use of special ammunition like Armor Piercing Discarding Sabot (APDS). In terms of shell size, for comparison, the APDS shell for the British 17pdr gun was just an inch longer at 34″ and could achieve 200mm of penetration, just under the requirements made. Some development might have been needed but effectively the AGF was looking at a gun not that different from the British 17 pounder firing ‘special’ AP ammunition.
The coaxial weapon choices give a little insight into the designer’s mindset as it includes several machine guns and a flamethrower. First, there were to be 2 coaxial machine guns, one .50 caliber and one .30 caliber both of which could be fired independently or together with the main gun, which was also to have a separate electrical firing system installed. Two more .30 caliber machine guns were to be installed “symmetrically located outside the turret in ballistic blisters so mounted as to fire coaxially with the main weapon” and yet another .30 cal fitted in the hull fireable by the driver. Not content with this array of machine guns the AGF stated that “consideration to be given to the mounting of bow machine guns or guns in remote-controlled ballistic blisters” and the artist’s impression seems to indicate the presence of two machine gun blisters on the front of the machine. One final machine gun was a .50 calibre anti-aircraft weapon to be installed on the turret roof fireable remotely by the tank commander and capable of being directed at ground targets if needed, presumably because the other 6 machine guns weren’t sufficient.
At least 6 smoke projectors in an armored housing were to be fitted to the outside of the tank fireable from inside and able to go out to 200 yards (183m). The final offensive weaponry was in the form of a swivel type flamethrower on the roof of the bow gunner’s compartment provided with traverse within the limits of his visibility and with a flame burst of not less than 30 seconds up to 1 minute. For defense, it is specified that fragmentation grenades must be deployable by crew to a range of 10 yards (9.14m) around the sides and rear of the tank without opening any hatches.
No less than 85 rounds of main gun ammunition were to be carried, along with at least 600 rounds for each .50 calibre machine gun, and 2500 rounds for each .30 calibre machine gun, 24 grenades, 6 smoke bombs, and at least 600 rounds of .45 calibre ammunition complete the logistical insight into ammunition supply.

Equipment

The main gun was to be stabilized horizontally and vertically for firing on the move. It was also specified that the coaxial weapons had to be stabilized at least 90% of the time as well. A built-in 10x rangefinder linked to the gun was to be fitted along with a tank commander’s x4 or x6 sight with “provision… to lay the gunner on the target through the agency of the rangefinder”.

Another feature was that “the tank commander shall be provided with elevation and traverse controls that will follow the same response curves and shall override the gunner’s controls”. Finally, an auxiliary sight adjustable from x3 to x8 power and marked with various graduations to accommodate different ballistics of various ammunition types was used along with a 7 x 50 periscopic binocular sight on a rotatable plate for the tank commander. There was to be an elevation quadrant on the gun mount for the gunner, and all of this was supposed to be ‘rugged, simple, and accurate’ and unaffected by engine vibration.
The 360-degree rotatable turret would be fully balanced and fitted with both a power and a hand traverse with not more than 200 lb.ft. (271.16 N.m) of torque required to traverse it. Other issues for the turret were that it was to be sealed from weather and, like the hull, sealed from harmful gasses. Armored covering would cover the vision openings and the design shaped in such a way as to minimise ricochets from the turret into the roof of the tank. During travel, a sturdy travel lock would be used to secure the main gun.

Automotive

The improved Medium Tank was to be fitted with power steering and independently sprung wheels with shock absorbers over which would run a center-guide type track with a rubber bogie surface and integral grousers. The track lifetime had to be at least 3000 miles. It was specified that it also had to be suitable for climbing a 60% grade slope in damp clay.
The engine was to be a multifuel engine which would have to be developed specifically for it and capable of running on standard military fuel, oil and lubricants. It had to produce at least 20 horsepower per ton and cause minimal vibrations. Ease of maintenance was important along with a 5000 miles (8047 km) / 500 hours overhaul interval. The transmission would be either an “infinite ratio type” or fully automatic and if a clutch was to be used it had to have a long life and be free from dust. Whichever system was used, it had to have a high reverse speed.
Twenty horsepower per ton with a weight at 45 tons was implying an engine producing 900hp and such an engine did not exist for them, the engine in the 46 ton M26 Pershing, for example, was just 500hp.
As if the other requirements for the engine were not unrealistic enough the tank was also to have enough fuel for a cruising range of at least 100 miles (161 km) and the expectation was for a top speed on the road of not less than 20 mph (32 kph) sustained.

Miscellaneous Notes

In terms of stowage, this new tank would carry not less than 3 days of crew rations, a minimum of 5 gallons (18.9 litres) of drinking water (preferably 10 gallons / 37.9 litres) along with standard pioneer tools, spare parts and a 12 unit first aid kit in an armored external box.
The radio would be fitted as specified by Army doctrine along with a fixed fire extinguisher system and a positive pressure ventilation system for the crew. In the event of a failure of this system a door could be opened from the crew compartment to the engine to draw in air through the hatches for the crew that way.
Easily openable hatches were to be wide enough for crew in winter uniforms, seats to be adjustable, non-skid surfaces were to be used inside along with no sharp corners or projections. All instruments had to be operable while wearing gloves, and an escape hatch was to be fitted in the hull floor. Other features would include a red/white interior light, illuminated instrument panels, and the maximum use of alloys to save weight.
Exterior lighting was to be exactly that of the M4 series and the tank was to be easily towable with a temperature operating range from -10F (-23.3 C) to +120F (48.9 C) and wind speed up to 40mph. With winterization the vehicle would be suitable to operate down to -40F (-40 C).

Artist’s impression of the ‘Improved Medium Tank’ from AGF Report June 1945. The relevance of the square squares drawn on next to each machine gun is not known.

Conclusion

Looking at the specifications for the tank it is easy to see that a considerable amount of experience has gone into them. Crew comfort from seats to avoiding sharp corners and the use of gloves etc. all feature and yet still the AGF managed to add in a simply ridiculous amount of pointless items such as the superfluous machine guns scattered around the machine. The 3” gun specified might have been suitable for 1944 when it was first being considered but it was already going to be outdated by the time it could have entered production if it was approved.
Whatever the thinking was it was redundant. A new board under General Stilwell had convened in November 1945, known officially as the War Department Equipment Review Board (unofficially known as the Stilwell Board), to consider many of the same issues the AGF had. By the 19th January 1946, the Stilwell Board completed its own report and the idea for this tank was effectively dead. Any final hints of it completely disappeared by December 1950 when the requirements changed with the release of the Army Equipment Development Guide and the Army moved in a different direction with its medium tanks. The AGF’s Improved Medium Tank was consigned to history and mostly forgotten, the last grasp at a WW2 tank design.

AGF Improved Medium Tank specifications

Dimensions length not specified, width 3.4m, height – not specified
Total weight, battle ready 40,823kg (90,000lbs.) est.
Crew 5
Propulsion  20 horsepower per ton, ~900hp desired
Suspension
Speed (road) Not less than 32 km/h (20 mph)
Range Not less than 161 km (100 mi)
Armament 3″ (76.2mm) gun capable of penetrating 8″ (203.2mm) at 30 deg. at 1000 yds. (914.4m) with at least 85 rounds
Coaxial .50 calibre machine gun with at least 600 rounds
Coaxial .30 calibre machine gun with at least 2500 rounds
Symmetrically mounted .30 calibre blister mounted external machine guns with at least 2500 rounds each.
One .50 calibre AA machine gun with at least 600 rounds.
At least one .30 calibre hull machine gun (possibly two in blisters) with at least 2500 rounds each.
Smoke projectors with 6 bombs.
24 fragmentation grenades.
At least 600 rounds of .45 calibre ammunition for crew weapons.
Swivel type flamethrower with 30 to 60 seconds of fuel.
Armor Hull front – 6″ (152.4mm) min, 8″ (203.2mm) desired
Hull sides upper – 3″ (76.2mm) on sponsons around fighting compartment
Hull side lower – at least 2″ (50.8mm) around fighting compartment
Hull sides behind FC – 1.5″ (38.1mm)
Hull rear 1.5″ (38.1mm)
Hull top front over FC – 2″ (50.8mm)
Hull top rear ¾” (19mm)
Hull bottom front under FC – 1″ (25.4mm)
Hull bottom rear ½” (12.7mm)
Turret front 6″ min., 8″ desired including mantlet
Turret sides 3″ (76.2mm)
Turret rear 2.5″ (63.4mm)
Turret top 1″(25.4mm)
Total production None
For information about abbreviations check the Lexical Index

Links, Resources & Further Reading

Patton – R.P. Hunnicutt
Firepower – R.P. Hunnicutt
Army Ground Forces Equipment Review – June 1945
Report of the Army Equipment Board – 1945
Faint Praise: American Tanks and Tank Destroyers during World War II – C.M. Baily

Impression of the AGF Improved Medium Tank by David Bocquelet
An impression of AGF’s ‘Improved Medium Tank’ by Tank Encyclopedia’s own David Bocquelet.