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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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