Categories
Cold War Canadian prototypes Coldwar American Prototypes

‘Cobra’ Light Cross Country Combat Vehicle (Cobra LCCCV)

USA/Canada (1950-51)
Light Combat Vehicle – None built

Prompted by the experiences of the terrible weather and terrain conditions during of the War in Korea (June 1950 to July 1953), in October 1950 the US Army began a collaborative project with the Canadian Directorate of Vehicle Development to produce a highly mobile tracked vehicle platform suitable for a variety of roles. A specific emphasis was placed on use in extremely poor quality ground which could otherwise not bear the weight of a large armored vehicle. Specifically, the purpose was defined as “to study armored warfare to ascertain armor’s probable role in a future war, especially as it may be affected by current trends in technology and tactics, new tank and antitank weapons and new methods of their employment”.

The task, therefore was a huge one. Creating a highly mobile, lightweight, tracked vehicle capable of being used for a variety of combat and logistics roles and able to operate at high speed in sand, snow, or mud.

The variants of the Cobra were various classified as ‘AC’ for an articulated vehicle, ‘CC’ for a conventional vehicle, and ‘AT’ for the articulated vehicle and troop carrier.

Overall Design

The front profile of the vehicles was to be kept as small as possible to ensure it presented as small of a target to the enemy as possible. The tracks on the other hand, would be as wide as possible, nearly touching each other under the vehicle. This removed most of the belly of the design, so that virtually all of the vehicle was above the tracks, unlike other designs, such as the Tracked Jeep or a modified Universal Carrier. The tracks would also be of a new ‘spaced-link’ design to save weight and consist of a main run with 4 road wheels driven from the rear with an additional pair of wheels and tracks, unpowered at the nose of the vehicle.

Comparison of standard track to the new spaced link type track. Source: Modified from Army Service Technical Information Agency Working Paper ATI 149375, 1951

Automotive

A final recommendation on the working paper was to investigate the use of a two-stroke multi-bank engine to replace the Hercules JXLD 140hp engine which had been selected. A new engine, it was felt, would reduce weight and improve performance and work had already been done on this subject for a prospective and later aborted 10 ton (10.1 tonne) light tank for which a 180 hp 1,000 lb (435 kg) multi-bank two-stroke unit had already been built in 1938 made from six separate 30 hp engines. Smaller, more powerful and lighter than the Hercules unit, switching to this type of engine would permit an armored roof or other protection to be added or simply improved performance for the Cobra.

Comparison between existing 140hp 6 cylinder 4-stroke Hercules unit and the desired 180hp 18 cylinder 2 stroke multi-bank engine. Source: Army Service Technical Information Agency Working Paper ATI 149375, 1951

Armament

The primary armament for the Cobra was to take the form of a recoilless rifle on multiple mounts. The weapons were to be kept loaded at all times when approaching a combat zone due to the time taken to reload it, but could fulfill both anti-tank and infantry support roles adequately.

The weapons selected had to be capable of engaging and destroying an enemy tank with a performance required on defeating 13” (330 mm) of armor plate at 2,000 yards (1,800 m), although accuracy would be assessed at 1,000 yards (910 m) temporarily for the study. As an absolute minimum, anti-armor performance had to at least meet that of the T124 76mm anti-tank gun. In particular, the vulnerability of airborne troops to Soviet armor after being landed meant that the primary user for the anti-tank capability would have to be designed around the US airborne force.

American T124 76mm Anti-Tank gun. Photo: Lovett Artillery Collection

With a desire for at least a 75% fire round hit (with 15 seconds to aim at a target 2.3 metres square at 1,000 yards) being estimated as required to take out an enemy tank before it could fire back and no chance of a second shot in time, multiple recoilless rifles were needed, meaning a minimum of two guns were needed. The two guns considered being the 105 mm M27 rifle (formerly the T19) firing the T-43 High Explosive Anti-Tank (HEAT-T) round at 1,250fps (381m/s) or the newly proposed T136E2 or T137 BAT (Battalion Anti-Tank) gun firing a fin-stabilised projectile at 1,750 fps (533 m/s). With stadiametric range determination with two guns the chances of this first round hit increased to 79%, but this was considered to be an insufficient margin of error. As the Cobra carried almost no armor, it would have to destroy the enemy target first as it could not take any hit in reply.

Three guns firing the T-43 HEAT rounds using stadiametric range determination with one gun firing first and then the second two firing as a pair yielded an increased hit probably of 81%. However, the most effective combination was seen to be four of the then new BAT guns using the same ranging method which increased the probably to 95% at 1,000 yards (910 m) and 75% at 1,280 yards (1,170 m). This unusual method of one shot-adjust-salvo fire was seen as being more cost effective and simpler than the use of a dedicated range-finder which was considered expensive, difficult to adjust, and complex to train with. Multiple salvoes were simple, cheap, and provided a better margin of error. It should also be noted that although the report did not discuss projectiles other than the T-43 HEAT-T round, the M27 rifle could also fire the T268 High Explosive (HE, standardised as the M323), T-269 White Phosphorus (WP, standardised as the M325), T139 High Explosive Plastic (HEP-T, standardised as the M345B1) and M326 High Explosive Plastic (HEP, standardised as the M326) rounds. The BAT was to be an improvement over this M27 105mm rifle, lighter by 61 kg and despite being a ‘rifle’ was actually smooth bore.

The working paper concluded that, with regards to guns, further work should be conducted on improving the muzzle velocity of recoilless rifles in service and that more data should be obtained from firing trials under realistic combat conditions.

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Hit probability based on the three types of ranging. Source: Army Service Technical Information Agency Working Paper ATI 149375, 1951
Salvo based hit probability for the M27 recoilless rifle. Source: Army Service Technical Information Agency Working Paper ATI 149375, 1951

Armor

Not more than 20% of the weight of the vehicle was to be spent on armor with the heaviest protection concentrated at the front. The armor basis selected was steel ⅝” (16 mm) thick with a maximum of ¾” (19 mm) on the front of some variants. The armor was extremely thin, resistant at best to heavy machine-gun bursts, small arms fire, and shell splinters from 105 and 155mm guns. An alternative ‘light’ basis for armor of just ⅜” (9.5 mm) was also drawn up for the AC-1 design merely to serve as a comparison to the Tracked Jeep and to a modified Universal Carrier. The two thicknesses ⅜” and ⅝” respectively were also considered to be the minimum required to protect against .30 calibre and .50 calibre machine-gun fire but the ⅝” was considered to give the greatest margin of error for protection and was the overall recommendation for armor basis. This provided, according to the designers, complete protection to the front from the .50 calibre M2 Armour Piercing round at 2,930 fps (890 m/s) at any range and to the sides from 350 yards (320 m) for the AC-2 to 1,100 yards (1,000 m) for the CC-2. One final unusual note on the armor was that the hull sections were to be completely cast rather than welded to save weight.

Configurations

With the articulated (AT and AC) form of the vehicle, the engine sat longitudinally on the right hand side with the driver sat alongside it, in a semi-supine position on the left. This front section of the vehicle held only the driver and engine, behind which was the articulation mechanism to the back half of the vehicle. The back half varied between the various roles to be performed but was also driven by the same engine with the drive sprocket at the front.

Moving large numbers of troops across long distances over rough or boggy terrain with some protection from the elements and enemy fire features prominently in the Cobra design. Various sizes were envisaged for the troop carrier version for 6, 8, 10, and 12 men, in the form of the AT-6, 8, 10, and 12 respectively. The single crew member was sat in the front compartment with the crew section located behind him in the articulated portion of the vehicle. No armament was drawn and the seating positions as shown suggest no option for crew served weapons or firing ports but the report made clear that such weapons could be mounted as desired later. Armor was very thin, just ¾” at maximum, which would be sufficient to protect against heavy machine-gun fire across the front. Even the largest and longest (AT-12) version weighed in at just over 12.25 tonnes which, combined with the very long and wide track run with 610 mm wide tracks would produce a very low ground pressure.

The troop transports had light protection over the sides and none over the top. Removing the roof would allow the troops to fire over the walls and also significantly reduce the weight of the vehicle. At a later date, when other weight savings (particularly the engine) were found, a roof of up to ⅜” thick was considered.

Source: Army Service Technical Information Agency Working Paper ATI 149375, 1951
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Cobra AC-1 Source: Army Service Technical Information Agency Working Paper ATI 149375, 1951

The Cobra AC-1 used a rear-half with 7 wheels and the turret mounted right at the front of this section. Two recoilless rifles were to be mounted on each side with the gunner sat between them. To reload, the third crew member could elevate a protective box at the back to access the venturi at the back of the rifles. This system had the advantage of protecting the loader, but on the other hand, the significant disadvantage that even if only one round had been expended no further firing could take place during reloading on the first rifle. Twenty rounds of ammunition for the rifles was carried in the centre section of this rear portion of the machine permitting up to 5 full salvoes to be fired.

Cobra AC-2 Source: Army Service Technical Information Agency Working Paper ATI 149375, 1951

The Cobra AC-2 was shorter than the AC-1 and the rear portion was just 5 road wheels long instead of 7. The turret was moved to the rear instead with the 20 rounds of ammunition stored ahead of it at the front of the section. This arrangement had the advantage of shortening and lightening the rear section but made reloading even more complex, in that the turret would have to rotate fully to the rear in order for the loader (now sat in front of the turret) to reload the rifles from behind.

Cobra AC-3 Source: Army Service Technical Information Agency Working Paper ATI 149375, 1951

The Cobra AC-3 sought a different solution to the armament mounting with just 3 rifles mounted in parallel to each other across the left hand side, to the centre line of the rear portion of the vehicle. The gunner and loader sat on the right alongside these guns with the gunner at the front facing forwards and the loader behind him facing inwards towards the guns. Eighteen 105 mm rounds were then stowed under these rifles for the loader permitting up to 6 full salvoes. The mounting for the gun was limited to just 30 degrees each side in this arrangement.

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Cobra CC-1. Source: Army Service Technical Information Agency Working Paper ATI 149375, 1951
CC-2. Source: Army Service Technical Information Agency Working Paper ATI 149375, 1951

The Cobra CC arrangement was classed as ‘Conventional’ as it was not articulated. Unlike the articulated variants with the engine on the right and driver on the left, this arrangement was to have the engine lying centrally down the middle of the vehicle with the driver on the left and additional crew member on the right. The CC-1 design was just two man but the CC-2 had a third crew member sat in a small turret at the back. Both versions featured four rifles but reloading was much easier on the CC-2 due to this third crew member although it was consequently a longer and heavier vehicle. Seven road wheels were needed on the CC-2 compared to just 5 on the CC-1 and about 2.5 to 3 tonnes heavier depending on whether the CC-2 was to carry just a pair of guns or four. Both designs would be able to carry 12 rounds for their guns though, sufficient at least for 3 full salvoes.

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Four other drawn variants on the articulated platform Cobra. Mortar, AA, Rocket launcher and Cargo versions. Source: Army Service Technical Information Agency Working Paper ATI 149375, 1951

Other Cobra LCCCV variants

With a capable off-road platform, the Cobra would be available for use as a mortar carrier, an anti-aircraft vehicle (drawn mounting a quad .50 cal. AA mount), a rocket launcher vehicle, a cargo carrier (with a 3.5 tonne trailer), an ambulance, communications vehicle, and even a flame-thrower vehicle, although the ambulance and flamethrower vehicles were not drawn.

Conclusions

Three versions of the Cobra were recommended for construction. The AC-2, the CC-2 and the AT-12 were seen as comprising the best ideas for the platform across its combat uses. Sadly, none of these vehicles appears to have found its way into production. The Army would keep using its Weasels for transport in place of the Cobra and, although there were some other vehicles which did enter production with multiple recoilless rifles, such as the famous M50 Ontos, none of these Cobra vehicles made it to production. The articulated vehicle design idea did not go away however, and the most famous of this type of vehicle in use is the Hagglunds BV206.



Illustration of the ‘Cobra’ Light Cross Country Combat Vehicle (Cobra LCCCV) produced by Yuvnashva Sharma, funded by our Patreon Campaign

Sources

Army Service Technical Information Agency. (1951). Working Paper ATI 149375: Analysis of a Light Cross Country Combat Vehicle ‘The Cobra’.
Lovett Artillery Collection
US Army Materiel Command. (1976). Engineering Design Handbook: Recoilless Rifle Weapon Systems.
US Army (1951). TM9-329 105mm Rifle M27, 105mm Rifle Carriages M22 and T47 Modified and 105mm Rifle Mounts M75 and T143.
US Army. (1952). T/O&E 7-15 M27 105mm Recoilless Rifle
Rayle, R. (2006). Random Shots: Episodes in the Life of a Weapons Developer. Merriam Press


Categories
Cold War Canadian prototypes

Modified Tracked Jeep

Canada (1950s) – None Built

Every army, at some point, has to get around to tackling the design of a utility vehicle. These are small, mobile vehicles for a variety of roles, from hauling troops and supplies, to towing field guns, and even for combat. The small 4-wheeled utility vehicle known as the Jeep fulfilled many of these lighter roles during World War 2 as did the not-less-famous Universal or ‘Bren Gun’ Carrier. Both saw extensive use and modification to the extent that Universal Carrier and Bren Gun carrier are used as interchangeable terms and ‘Jeep’ became synonymous with an off-road vehicle.
What is less well known is that the Canadians did an extensive amount of work of their own for a tracked utility vehicle during the War. This was known as the ‘Tracked Jeep’; effectively a go-anywhere multipurpose tracked vehicle made with a lot of components from Jeeps. This small vehicle would be able to be borne by gliders for use by airborne troops and fulfill various support, logistic, and scout functions and had entered prototype testing by 1944. Orders placed in 1945 though were delayed in production and by the end of the War, the Tracked Jeep project was effectively dead, although some testing in the very marshy conditions of northern Canada’s Manitoba province provided useful information for later tracked developments. The primary author of this work was Major M.G. Bekker of the Canadian Army who worked for the Canadian Directorate of Vehicle Development.
Major Miecyslaw Gregory Bekker was a Polish emigree who had worked for the Polish Ministry of Defence from 1931 until 1939. In 1940 he was working for the French Ministry of Armaments, but with the Fall of France, that position did not last long, and by 1943, was living in Canada and working for the Canadian Military until 1946. His speciality was off-road traction and all-terrain vehicles and by 1950 was working on secondment for the Canadian military at the Stevens Institute of Technology in Michigan. He would later go on to become head of general mobility with General Motors Corporation, meaning that this highly experienced and well-travelled engineer could even have had a hand in the early stages of what became the US HMMWV program.

Canadian Tracked Jeep Pilot No.1, May 1944. Photo: MilArt blog
The lessons learned from the design were not forgotten though, and in 1950, with the Korean War (June 1950 – July 1953) starting, the US and Canadian authorities worked together on a new series of highly mobile tracked vehicles, and in doing so, looked back on developments including the experience from Canada with the Tracked Jeep. By 1950 though, the Tracked Jeep of WW2 had substantially evolved and was now more of a tank destroyer than a utility tractor.

Front and side views of the Tracked Jeep circa 1950. Source: Army Service Technical Information Agency 1951

Design

The Tracked Jeep name had been kept, but the old suspension of 5 small 12 inch (300mm) diameter wheels had been abandoned in favour of a much simpler big-wheel design. The new design featured four much larger diameter wheels about 24 inches in diameter (600mm) with three of them in contact with the ground via the tracks, and the fourth at the front providing the drive. The rear-most wheel was on a trailing arm and was also provided with a large spring for suspension. The other wheels were sprung individually, horizontally.

Original suspension on the Canadian Tracked Jeep Pilot No.1, May 1944. Photo: MilArt blog

Improved suspension arrangement for Canadian Tracked Jeep showing the three ground contact wheels and rear trailing arm spring. Source: Army Service Technical Information Agency 1951
This tracked Jeep bore little or no resemblance to the older one. The hull one was different too. In place of the clean lines of the 1944 vehicle, this new 1950 vehicle was much more angular and now sported a turret. Not a full turret, but an unusual offset turret mounted on the rear right-hand side of the vehicle with limited 30 degrees traverse to the left and right. One similarity with the original tracked jeep though, was the retention of the original Willys Jeep engine, although as the original design had switched to the more efficient Carmazin radiator, it is likely this 1950 version retained that improvement too.

Crew

This diminutive vehicle was to have a crew of just two. A driver, located in the front left, and the overworked commander/gunner/loader in the rear centre sat facing outwards towards the breech of the rifle with the ammunition for the gun stowed behind him.


Illustration of the ‘Modified Tracked Jeep’ produced by Yuvnashva Sharma, funded by our Patreon Campaign.

Protection

The hull of the Tracked Jeep was just 112” inches long (2.84m) extending to 134” (3.4m) to the end of the gun barrel which overhung the front of the vehicle. The vehicle was light too, just 6,400 lbs gross weight (2.9 tonnes), but this was at the expense of protection. The armor was seriously thin with just 5/16” inch (8mm) at the front and ¼” (6.4mm) on the sides, making the vehicle barely bulletproof to normal small arms and not able to withstand machine-gun fire.
The small size of the vehicle (just 2.84m without the gun and 3.4m with it pointing forwards) was a very important factor. and could be reduced by stowing the gun at an angle across the hull to the front left corner). The vehicle was just 73” inches (1.85m) wide and 64” inches (1.63m) high and under 3 tons, meaning it was small enough and light enough to fit in every transport aircraft and glider in service at the time.

Armament

The advantage of this small vehicle was the armament. This design would provide a highly mobile platform, ideal for airborne troops with firepower to match. This firepower was in the form of a single 105 mm recoilless rifle. Assuming this to be the American M27 rifle, this would be able to fire the T-43 High Explosive Anti-Tank (HEAT-T) round at 1,250fps (381m/s), as well as the T268 High Explosive (HE)(standardised as the M323), T-269 White Phosphorus (WP)(standardised as the M325), T139 High Explosive Plastic (HEP-T)(standardised as the M345B1) and M326 High Explosive Plastic (HEP)(standardised as the M326) rounds. Only eight rounds could be carried in the vehicle though, limiting its usefulness for infantry support. If American practice was followed, this would be increased to 9 as the weapon was expected to be carried loaded into a combat zone.
There were three types of ranging available for the main gun from plain visual ranging, to stadiametric ranging, and finally, a rangefinder. With just a single shot, the estimated accuracy for a first shot hit with this weapon assessing those three types of range-finding was assessed in 1951 as 8%, 18%, and 49% respectively at 1000 yards (914 m). It should be noted too that the High Explosive Anti-Tank (HEAT or HEAT-T) round was capable of defeating 13” (330 mm) of armor plate which meant it was able to defeat any tank then in service.
The small turret in which the main gun was housed is shown in data tables as having 60 degrees of traverse with 30 degrees each side, however, a measurement of the blueprints shows, only 30 degrees to the right and just 21 degrees to the left for a total of 51 degrees. Elevation and depression are not stated but are measured from the blueprints as -10.5 degrees to +30 degrees.

Plans of the Tracked Jeep circa 1950. Source: Army Service Technical Information Agency 1951

Conclusion

The tracked jeep was not a bad concept in 1944 and it was still a viable concept in 1950, but it had very little growth potential. The vehicle was not really much more than a universal carrier with a very lightly protected superstructure and a recoilless rifle. That rifle could and was already easily fittable on a normal wheeled jeep or onto almost any other tracked vehicle. The small size, two-man crew and lack of ammunition with just 8 rounds meant that the tracked jeep of 1950 was not heavily armored enough to withstand enemy counterfire and not well-armed enough to provide sustained fire support in battle. As such the project was discontinued, the merits simply did not outweigh the problems and other solutions were available.

Specifications

Dimensions (L-W-H) 112” x 72” x 52”(2.84m x 1.8m x 1.32m)
Total weight, battle-ready 6,400 lbs (2,900kg)
Crew 2 (Driver, Commander/Gunner/Loader)
Propulsion Willy’s 4×4
Suspension Torsion Bar
Speed (road) 36mph (road), 6mph (cross country)
Range 140 miles (road), 50 miles (off-road)
Armament 1 x 105mm recoilless rifle – 60 degree traverse, 8 rounds
Armor ¼” armor basis (5/16” inch (8mm) at the front and ¼” (6.4mm) on the sides

Sources

Army Service Technical Information Agency. (1951). Working Paper ATI 149375: Analysis of a Light Cross Country Combat Vehicle ‘The Cobra’.
Hall. C. (2008). A Biographical Dictionary of People in Engineering. Perdue University
Lucy, R. (2014). Canadian Tracked Jeep (Willy’s). MilArt blog.

Categories
Cold War Canadian prototypes

‘Firefly’ Firefighting Tanks

Canada (1988-2000) – Firefighting Vehicle – None Built

Canada is a vast nation with enormous forested areas, so it is of no surprise that a variety of designs have cropped up over the years to fight forest fires. For a vehicle firefighting in remote and rugged areas, good levels of mobility are required and so it is also no surprise that tracked vehicles are particularly well suited for the sort of job in question.
Likewise, the use of jet-exhaust for firefighting activities is not a completely new concept, nor is the repurposing of old tanks for civilian usage.
The real question is, has anyone ever combined a surplus tank with jet engines for fighting fires? Surprisingly to many, the answer is yes. There was a T-34 tank hull with jet engines used in the aftermath of the 1991 Gulf War, where the force of the jet exhaust could blow out the oil wells left burning by retreating Iraqi forces. Less known is a daring idea from 1998 in Canada using a similar principle.

The Name

First and foremost, the use of the name ‘Firefly’ has to be addressed. Despite it including the word ‘fire’, neither the Sherman nor Churchill tanks used in this Canadian modification were ‘Firefly’s’ in the tank sense of the word, that is, fitted with the 17 pounder gun, which clarifies some of the confusion over which version of tanks are being described.

The hull selected for this version appears to be that of an M4A3(76)W HVSS Sherman and is described (but not shown) as using the trailer for water and fire retardant. Source: Patent CA2242736.

The Design

The design for the Firefly tank was submitted by Robert Matheson of Edmonton, Canada on July 1988 and covers the use of a ‘Turbine Jet Engine-Army Tank Forest Fire-Fighter’ described as:

“an apparatus which will enable the user to fight forest, brush or grass fires by injecting water or another fire retardant into the high pressure large volume of air being exhausted from a turbine jet engine mounted on the turret of an obsolete army tank which provides the required with, mobility and ability to direct airflow from the jet engine by use of the rotatable turret”

The description is therefore simple and explanatory but requires some elaboration. The tanks to be used are not necessarily Shermans or Churchills, as shown in the patent, but are an indication that any surplus or obsolete tank would be fit for the purpose.
It should also be noted that, although Canada did use Churchill tanks, and Firefly’s and Crocodiles and Shermans at various times, they did not operate the M4A3E8 shown in the drawing domestically, they only operated M4A2E8’s.
The tank itself should be selected because it has the mobility to go off-road for firefighting and because the mass of the vehicle means that the back pressure from the use of the jet turbine would not cause it to lift off the ground. Mounting the turbines onto the turret also adds the ability to turn and direct the blast of air/water in any direction. The only modification other than the addition of the two jet turbines to the turret was the removal of the gun from whichever tank was selected. No additional heat insulation for the vehicle or cooling system was envisaged, relying instead on the vehicle to provide inherently some “substantial protection from the heat of the fire to allow the operator to attack the fire where such action would be most effective”.


Artists impression of the Churchill-based ‘Firefly’, based on existing drawings.


Artists impression of the M4A3E8-based ‘Firefly’, based on existing drawings.

Both of these Illustrations were produced by Alexe Pavel, based on work by David Bocquelet.

Critique

The use of aircraft to fight forest fires is a very expensive endeavor and depends on the weather conditions at the time. Fire trucks struggle to go off-road and further struggle to deliver a sufficient volume of water to stop a fire. With a particular emphasis on the protection of buildings at the margins of the forested areas, these Firefly vehicles would be able to deliver a large quantity of water and fire retardant like AFFF at high pressure injected into the exhaust of the engine blasted at the fire.
The example vehicles on the patent were both drawn or described equipped with a trailer carrying water and fire retardant. However, the quantity of liquid in such a trailer would be just a fraction of what would be needed to make a difference to a forest fire. There was only brief consideration of a direct hook-up to available mains supplies of water or pumps feeding water from a stream or lake described as “a means could be readily provided to have the ability to supply a constant supply of water”. In this regard, the design is a failure, as even if it gets to the fire in the right place, it would not be able to sustain operations long enough to make much of a difference. The reuse of the existing Churchill (A.22F) Crocodile fuel trailers would indicate a volume of water of about 400 Gallons (UK), (1,818 liters) but the drawing also clearly shows the Firefly trailer is at least twice as small as the Crocodile one relative to the tank. Perhaps as much as 1000 Gallons (UK) (4,546 liters) could be carried, although this would not last very long pumped into the exhaust to fight the fire.
Fires are hot. This may seem obvious, but tanks are made of metal and riding in a hot metal box would be an exhausting experience. With the operators of the tank most likely having to be inside the vehicle with the hatches shut, the temperatures may well have become intolerable, and there is no discussion of additional cooling or air-handling systems provided to ensure that the operators did not succumb to the heat and stifling conditions inside.

Churchill Mk. VII (A.22F) version with modified Crocodile trailer. Source: Patent CA2242736
Attaching the turbines to the turret causes additional problems. The weight of these jet turbines would likely overstress the ability of the turret motors to rotate the turret properly, and even if they did not, the pipework connections would prevent a full range of motion. The force from the turbines would also cause a lot of stress on the turret ring as well.

Conclusion

The idea of attaching jet-turbines to tanks is definitely possible and had been done before, as had the idea of using them for fire-fighting purposes. This plan was no doubt well-intentioned and did combine the elements needed for firefighting, but overlooked some key design and operational hurdles, not least of which being that regardless of the technical merits of the design, who was going to pay for the operational costs and maintenance of these obsolete tanks. Presumably, lots of these modifications would be needed in every province due to the slowness of moving them from A to B and the vast landmass of Canada. Hazards to the crew from smoke and heat were inadequately addressed and there was insufficient consideration given to providing a sufficient supply of water for sustained operations. Other matters, like whether it was advisable to blast a fire with air at high velocity possibly adding to the spread of burning embers was not discussed at all. The final note should, of course, be the tanks. Yes, it is true the design is shown using a Sherman and a Churchill tank and, whilst these might be amusingly anachronistic, they are only indicative of how such equipment would look on a surplus tank. Whilst the design has no military value and a questionable value for civilian purposes, these designs are probably more interesting to model makers today.

Source

Canadian Patent CA2242736, filed 7/8/1998, granted 1/8/2000

Categories
Cold War British Prototypes Cold War Canadian prototypes Coldwar American Prototypes

FV4201 Chieftain/90mm Gun Tank T95 Hybrid

USA/UK/Canada (1957-59)
Main Battle Tank – none built

ABC Countries

By the end of the 1950’s, tank development in both the UK and USA was becoming more streamlined with fewer outrageous ideas for atomic or super heavy monster tanks. The ‘Main Battle Tank’ concept had taken hold by 1957, inheriting the role of the medium tank. Heavy tanks were still seen, certainly in the US, as being the ones to take out the heaviest enemy armor but soon too that role was subsumed into the duties of the MBT.
The Soviets weren’t much for caring about such things and still had their own heavy tanks and well protected medium tanks which were causing consternation in the West. The Western powers lacked parity in both numbers and quality with the Soviets and both the US and UK had identified the need for a new medium tank for the 1960-1970 era. The United Kingdom, for instance, was still using the Centurion tank (a WW2 era design) and the USA, which was using the M48A2, was still developing the tank which would eventually become the M60.
In the short term, the UK would up-armor and up-gun their Centurions to meet the perceived threat of the Soviet T-55 tank until their own new tank, the FV4201, could enter production.
The FV4201 is better known as ‘The Chieftain’ and, despite being near the end of its development, many features still had not been settled on. The US equivalent program, the T95, was typical of US programs, an enormous entanglement of overlapping developments and was busily trying to encompass all of them. The project was still fairly new, however, with prototype hulls only authorised to be constructed in 1955. Thus, from 1957 to 1959, there were basically two tanks under development, the British Chieftain, which was nearing completion, and the American T95 which had only just started.
The United Kingdom, Canada, and the United States were already liaising closely in the new Cold War era on a variety of developments and tank design was not omitted from this. Work between the United States, the UK, and Canada, known as the ‘ABC’ countries (America, Britain, & Canada), had even achieved some degree of interchangeability and standardization for tank programs by 1957. Programs which had been fulfilled were standardization of the British 105mm gun, the British 120mm gun, an American version of the British 120mm gun, the American 105mm T254 and 120mm T123E6 guns, and three projects related to the FV4201 and T95.
These were:
-Mounting the FV4201 turret on the T95 chassis
-Fitting the US T208 90mm gun in the FV4201
-Mounting the US T95 turret on the FV4201 chassis
It was noted though that “in order to permit the FV 4201 turret to be mounted on the T95 hull, the U.K. consider modifying their turret ring with the T95 hull mounting surfaces”. It was agreed that “if the U.K. ring can be made interchangeable with the U.S. ring in respect to mounting surfaces on the hull, it will be possible to mount the complete turret providing major modifications are made to the turret basket”. The major modifications being that the British turret basket was too big for the T95, a smaller turret basket would be needed which would reduce significantly the amount of ammunition which could be carried. Even so, the expectation was that the T95 with a reworked 4201 turret and basket would carry at least 50 rounds of main gun ammunition. The panel reviewing the situation were adamant that all medium tanks must have ready rounds “stowed in the turret fighting compartment… in a favorable position for rapid loading of the main armament”.
That was not the end of the problems with the idea though. The turret bustle of the 4201 masked the air louvers on the T95 hull which “would undoubtedly affect the engine cooling”. One curious note records that one issue was that the driver’s periscope on the T95 hull interfered with the 4201’s gun mantlet. Exactly what this means is not clear as the FV4201 turret design was mantletless.

Guns

The British FV4201 was scheduled to enter production in 1962 with an expectation of prototypes available for trials by 1959. This new British tank meant to replace the Centurion was to mount a 120mm main gun using bagged charges. A lightened version this gun was also in development in the USA to weigh just 4156 lbs.(1885 kg). Since the initial specifications for the FV4201 were provided in the 1957 conference the design had changed slightly, improving the hull armor slope and the depression of the main gun (in a mantletless type turret) was improved from -7.5 degrees to -10 degrees.
The FV4201 turret would not be able to mount the T123E6 120mm American gun though as the weight would put the turret out of balance but it could mount the US 90mm instead. To do so would involve the use of an adaptor sleeve and the mounting surfaces of the gun but this was seen as having value for the tank in the short term.
On the other hand, the British 120mm bagged charge gun could be mounted in the T95E1 turret with only minor modifications made to the gun mount albeit at a weight increase of 1600lbs. (725.7kg). Of note here is that the T95E1 turret was the fifth turret in the American T95 program. When the T95 chassis was chosen to be common to both medium and heavy tank programs, five more chassis (for a total of 9) were ordered along with this turret. Four of those chassis went to the heavy gun tank program but as that program had no turrets ready three of the chassis were expediently fitted temporarily with existing turrets just for automotive trials. The remaining chassis got this new fifth turret and therefore was designated T95E1 to differentiate it from the others. The mention in the conference specifically for T95E1 can only, therefore, relate to this vehicle.

Medium tank guns

The 90mm T208 gun mentioned could fire the T320E60 APFSDS-T rounds at 5,200fps (1,585 mps) and defeat 5″ (127mm) of armor angled at 60 deg. at a range of 2000 yards (1828.8m). The other gun mentioned in the Tripartite Meeting on Tank Armament is the American 105mm T254 which is a lightened version of the British 105mm gun. The T254 was known to fit in the T95 turret, although “it is not planned now to install this gun in this type of turret since the installation is not ideal from the standpoint either of turret balance or turret configuration” but would be mounted on a T95 for test purposes (which would be known as T95E5). The advantage of the T254 gun was that if that gun became the standard US medium tank gun then it would be able to utilise the same ammunition as the up-gunned (105mm) British Centurion (assuming a suitable primer for the shell was selected). The Canadian contingent considered it “highly desirable that the gun and ammunition [for medium tanks] be standardized. To this end, the 90mm smooth bore can be placed in the FV4201 and the T95 turret modified to accommodate the 105mm X15 and possibly the UK 120mm bagged charge gun”.
The Canadians were anxious to see comparative firing trials between these two guns and to make an objective decision on their choice for a new medium gun tank although both were expected to exceed the requirement to defeat 120 mm of homogeneous armor plate at 60 deg. at 2000 yards which had been agreed as the standard at the Third Tripartite Conference.

Armor

Like the FV4201, the T95 was to use cast sections of armor for the nose with the sides and floor made from armor plate welded to the cast sections. This was a departure for the Americans who had already been using an all cast hull for the M48. The entire T95 turret was cast armor but the FV4201 turret was only cast in the front with the other sections made from plate armor welded on.
Overall, the T95 was expected to be a significant improvement over the M48A2’s which were already in service as “for example, the latter [M48A2] can be defeated from the direct front by the US 3000fps [914.4mps], 90-mm AP projectile on the upper hull front from 125 yards [114.3m] and on the turret front from within 1,550-yards [1,417.3m] range. The new medium gun tank, on the other hand, cannot be defeated from the front by this projectile”.
It was further theorized that the frontal armor was sufficient to defeat a theoretical Soviet 100mm AP shell traveling at 3,500 feet per second (1066.8mps) at 1,500 yards (1,371.6m) across a 60-degree arc. The armor was considered deficient, however, in terms of protection for the engine deck, sides, and rear, as well as having defective floor armor insufficient to protect from high-pressure mines. A final note on the protection for the T95 was the consideration of siliceous cored armor inside the frontal hull and turret castings although this still had not been done by this time and did not form part of the consideration for the interchangeability of the guns or turrets.

The Canadian Intervention

The Tripartite meetings of the ABC countries featured many Canadian needs. They did not class themselves as a tank producer nation, just a user, but they also had specific requirements they wanted from the tanks they were being expected to purchase. Being able to purchase either UK or US tanks effectively meant that the Canadians could be selective with what they wanted and expect that anyone who wanted to sell tanks to them would meet their demands.
For the new medium gun tank, they had agreed back in 1955 to the weight limit for this vehicle being set at 50 short (US) tons (45.36 tonnes). Both the T95 and FV4201 met this requirement, with the T95 being 20,000lbs (9,072 kg) under the weight limit.
The Canadians wanted standardization of guns, ammunition and gun mountings. They also demanded that any gun chosen had to meet the 120mm/60deg./2000 yard standard and be used in comparative firing trials. There is a small irony here that neither the FV4201 nor the T95 actually had that level of protection themselves. Further, the Canadians noted that, in comparing the designs of these tanks, the US had placed their emphasis on reducing the size of the vehicle and that while the T95 had less protection against kinetic energy ammunition than the FV4201, it did have a higher level of protection against chemical energy weapons (HEAT rounds).
In estimating the performance of the guns on offer, they determined that the UK 120mm bagged charge gun appeared to be more effective than the US 90mm smoothbore. In terms of sighting arrangements, the Canadians also preferred the British system for gun control as it was simpler, making use of a ranging machine gun compared to the US which “was still developing complex arrangements in preference to the ranging rifle system”.
In a nutshell, the Canadians wanted the best of both worlds, they wanted the hitting power of the British gun combined with the lighter, lower, more mobile US T95 to which they recorded that “the UK gun in the US tank would seem to be the logical answer. It may be technically possible to mount the 120mm bagged charge gun on the T95. With such a combination we should, for once, achieve a qualitative superiority over the Russians”.
The T95 with British gun combination favored by the Canadians was eventually effectively created by the US T95E6 mounting the 120mm T123E6 gun although the British 120mm X23E2 gun or lightened US version of it were still possible for mounting. In the meantime, while those experiments and considerations were going on, the UK had already submitted drawings to the Americans for a cost analysis for the re-engineering needed to fit the T208 and T208E9 guns in the FV4201. As it turned out, this project too came to nothing.
R.P. Hunnicutt (Abrams) records that the British 120mm gun was eventually mounted in a T96 turret in Study F of the T96 program (this being the heavy tank program) although the bagged charge was not popular with the US testers leading to the proposal to adopt a new breech and combustible case ammunition for it instead. The Americans were suitably impressed with the British 105 and 120mm guns though. So much so they made their own versions of them and “these two weapons and the original British guns were superior for tank use because of their lethality combined with lightweight, relatively short tubes, and short rounds requiring less loading space”. The only drawback of using the 120mm gun in the T95 turret was the necessity for a single loader to handle the two-piece ammunition” although a loader assist mechanism was considered to make this concern moot. Either way, the Americans elected to move on to a single piece round and modify the gun accordingly.
That modified gun was then fitted into a T95 turret in Study G (back to the medium tank program) producing a balanced gun capable of being stabilized for firing on the move.

T96 Study F turret with British 120mm bagged charge gun fitted on T95 hull. Note the use of a mantlet.Source: Abrams by Hunnicutt
T95 Study G fitted with the American version of the British 120mm gun Source: Abrams by Hunnicutt

Conclusion and one last hybrid

After the T95 program had been abandoned, the turret interchangeability concept didn’t go completely away. An initial assessment was even carried out on the XM60 as to whether it could take the British turret, the conclusion was that it was possible although it would certainly have been an odd-looking tank. The end outcome of all of the interchangeability studies is hard to gauge. The British stuck with their bagged charge gun, the American eventually chose their own gun for their own use and the Canadians were left without the tank they wanted. The option the Canadians had chosen suited their needs better than either the T95 or FV4201 could on their own: plenty of hitting power with a much more mobile vehicle. The T95 program was eventually terminated and the Canadians didn’t take Chieftains, preferring the mobility and firepower of the up-gunned Centurion instead.
The interchangeability of the guns was in itself a good idea, especially for replacement in wartime and the British turret and guns were well regarded. The interchangeability of the turrets was not easily rectified though, the Chieftain was nearly at the end of development and the British were unlikely to completely redesign the turret basket when there was no perceived market. The Canadians, after all, found the T95 turret acceptable in its own right, they just wanted the better gun. So, at the end of all this work, the overall outcome was that the interchange of T95 and FV4201 was indeed possible.
The FV4201 needed some work on the ring and basket, to take the T95 turret and the idea of mounting the T95 turret on the Chieftain was an altogether bigger task which no one was interested in trying. The report terminated discussion of the matter saying “it appears unlikely that the US T95 turret can be mounted on the UK FV4201 chassis without a major redesign of components which cannot be contemplated at this time”. As a result of the problems involved in modifying turret rings to match each other and overlapping demands for which gun was preferable, the whole affair was terminated with no prototypes completed.
The discussion does provide a real insight into just how hard it can be to design a tank to suit more than one role and customer and the idea of swapping turrets from the T95 and Chieftain tanks or even the XM60 as well as a variety of gun options remains popular if not in military circles then at least in those of modellers.

T95/FV4201 hybrid (T95 with FV4201 turret) specifications

Dimensions Length – 426.1 inches (10.82 m) (est. based on T95E6)
Width – 124 inches (3.15 m) (within the 124 inch limit imposed by the Berne International Loading Diagram)
Height – >112 inches (2.84 m)
Total weight, battle ready >32 US short tons est.
Crew 4
Propulsion air cooled, 8 cylinder, 560 horsepower AOI-119505A with 4 speed hydraulic converter-type transmission providing at least 13.5 horsepower per ton
Suspension
Speed (road) 35 km/h est.
Range >150 miles (241.4 km) at 17.5 mph (28.2 kph) with  230 US gallons (870.6 litres) fuel
Armament various options
Armor Sectional cast hull with welded plate and sectional cast turret with welded plate sides, roof and rear
Hull front upper – 3.8″ @ 65 deg. (96.5mm) (to be equivalent to 4.4″ @ 60 deg. (111.8mm)  which is an increase of 0.4″ (10.2mm) over the M48A2 which was 4″ at 60 deg. (101.6mm))
Hull front lower – 3.2″ to 5.5″ @ 50 deg. (81.28mm to 139.7mm)
Hull sides – 1.5″ to 4″ (38.1mm to 101.6mm)
Hull rear – 1″ at 0 to 20 deg. (25.4mm)
Hull top – 0.8 to 1″ (20.3mm to 25.4mm)
Hull floor – 0.5 to 0.7″ (12.7mm to 17.8mm)
Turret – FV4201
Total production zero
For information about abbreviations check the Lexical Index

T95E1 with British 120mm gun (the Canadian Option) specifications

Dimensions Length – 426.1 inches (10.82 m) (est. based on T95E6)
Width – 124 inches (3.15 m) (within the 124 inch limit imposed by the Berne International Loading Diagram)
Height – 112 inches (2.84 m)
Total weight, battle ready 32 US short tons est.
Crew 4
Propulsion air cooled, 8 cylinder, 560 horsepower AOI-119505A with 4 speed hydraulic converter-type transmission providing at least 13.5 horsepower per ton
Suspension
Speed (road) 35 km/h est.
Range >150 miles (241.4 km) at 17.5 mph (28.2 kph) with  230 US gallons (870.6 litres) fuel
Armament British 120mm bagged charge main gun with at least 50 rounds
Armor Sectional cast hull with welded plate sides, floor and rear, and fully cast turret
Hull front upper – 3.8″ @ 65 deg. (96.5mm) (to be equivalent to 4.4″ @ 60 deg. (111.8mm) which is an increase of 0.4″ (10.2mm) over the M48A2 which was 4″ at 60 deg. (101.6mm)
Hull front lower – 3.2″ to 5.5″ @ 50 deg. (81.28mm to 139.7mm)
Hull sides – 1.5″ to 4″ (38.1mm to 101.6mm)
Hull rear – 1″ at 0 to 20 deg. (25.4mm)
Hull top – 0.8 to 1″ (20.3mm to 25.4mm)
Hull floor – 0.5 to 0.7″ (12.7mm to 17.8mm)
Turret (T95E1) front – 7″ at 60 deg. (177.8mm)(compared to the M48A2 with just 3.7″ at 60 deg. (94mm))
Turret (T95E1) gun shield – 15″ (381mm)
Turret (T95E1) sides – 3″ @ 45 deg. (76.2mm)
Turret (T95E1) rear – 2″ (50.8mm)
Total production zero
For information about abbreviations check the Lexical Index

Links, Resources & Further Reading

Report of the Tripartite Technical Conference on Tank Armament – October 1957
Abrams – Hunnicutt
Fourth Tripartite Conference on Armour – October 1957
Tank Factory – William Suttie


T95 hull with XM60 Turret and standard 90mm Gun.


The hull of T95 Pilot No. 2 with 90mm Gun T208.


FV4201 hull with T96 Study F turret and British 120mm bagged-charge gun, without fume extractor.


T95 hull with an impression of an Americanised FV4201 Turret with M48/M60 style commanders cupola and 120mm gun with fume extractor.


T95 Hull with the standard FV4201 Chieftain turret and 120mm gun.

All illustrations are by Tank Encyclopedia’s own David Bocquelet.