The M22 "LOCUST"
Light Airborne Tank

We are currently restoring an M22 "Locust" light tank from the ground up. The Locust was one of the smallest tanks used by the Allies in Europe during WWII. It was the first tank designed by the U.S. primarily for airborne operations. It was light in weight but was expected to add badly needed firepower to airborne forces.

DESIGN CONCEPT AND DEVELOPMENT

World War II strategists in the U.S. became aware of the effectiveness of airborne assault forces by studying German victories achieved in Europe. They were also aware of the vulnerability of lightly armed airborne infantry alone and behind enemy lines without direct support from a main force. Because of increasing interest in an air delivered light tank by experienced field commanders and the British, the Ordinance Department formulated a design concept requiring the development of a light tank that would aid airborne units during critical mission phases and be sufficiently light in weight to be delivered by airborne means. The light tank would support the airborne infantry until reinforcements from the main force arrived. In May of 1941 design began on the M22 Locust light tank at the Marmon-Herrington Company. Production began in April 1943 and ended in February 1944 with a total production of 830 tanks. Under lend-lease, 260 Locusts were given to the British. (more details below)

Our Restoration in Process

ENGINEERING CHARACTERISTICS

The M22 was constructed of steel plate using welding as opposed to riveting technology. Riveted construction methods had long since fallen from favor because of the disastrous propensity of rivets to bounce around inside the vehicle when the outside rivet head was sheared by anti-tank munitions. The front armor was 1 inch thick with the sides being approximately 1/2 inch plate. The sloped front and sides added additional protection by helping deflect projectiles upward. The armor is minimal because of stringent weight requirements limiting the vehicle to less then 16000 lbs. Weapons included a single 37mm main gun and coaxial 30 caliber machine gun. Original models of the vehicle had more machine guns which were abandoned in the final design because of weight limitations.

The box structure on the left front of the vehicle is the driver's hatch and vision port. The vehicle was equipped with M6 periscopes on the driver's hatch and the turret. The front drive sprocket was powered by the transmission unit and engaged a steel track. Four road wheels connected to a volute spring suspension provided support for the vehicle. The rear idler wheel provided minimal vehicle support and was used to control track tension. Ground contact pressure was 6.41lbs/sq.in., quite low for a tank. The vehicle dimensions are: length 12ft. 11in., width 7ft. 3.75in. and height 5ft. 8in. This resulted in an extremely tight crew compartment consistent with sardine style packaging. The low silhouette was somewhat unusual for American light tanks of the era and a decided advantage by offering a low profile to enemy gunners.

The 4 major lifting lugs on the side of the hull just above each road wheel suspension mount are for hoisting up under the belly of a C54 cargo plane after turret removal. The C54 cargo plane and British Hamilcar glider were the only means available for airborne delivery of the vehicle. The vehicle was powered by a Lycoming O-435-T six cylinder air-cooled aircraft engine yielding 162 hp at 2800 rpm with a maximum torque of 332 ft.lbs. at 2100 rpm. Like most tanks of the early war era, aircraft engines were used because of their high power to weight ratio. The tank had driving range of 110 miles with a full tank of 57 gallons of gasoline. Dual engine exhaust pipes merged into a single pipe and circular muffler.

The 6 cylinder opposed engine powered the vehicle at a top speed of 35 MPH. The engine was adapted to a large clutch/fan disk. The fan was required for cooling of the massive aircraft engine. A drop down gear box was mounted on the engine output shaft to bring the drive shaft close to the floor and allow room for the turret basket. The drive shaft was connected to a 4 speed transmission and differential unit at the front of the vehicle. The driver's seat is located to the left of the transmission unit. The driver essentially sits on the floor in very cramped quarters.

Two levers control the left and right brakes of the vehicle. Pulling the right lever turns the vehicle right while pulling the left lever turns the vehicle left. Pulling both levers stops the vehicle. Due to space restrictions the control panel is to the right of the driver above the transmission unit. The turret was manually operated, a primitive yet weight saving feature. Behind the drive shaft is the escape hatch mounted on the floor. The engine was equipped with dual ignition, typical of adapted aircraft engines of the day. Fuel delivery was through long induction tubes which made starting difficult. An elaborate priming system was installed to deliver fuel to each cylinder before starting. Typical ammunition used by the 37mm main gun includede high explosive rounds that had a terminal velocity of 2700 ft/sec at 1000 yards.

USAGE IN WORLD WAR II

Development of the M22 continued by the Ordinance Department, but engineering problems dealing with excessive weight and poor performance were encountered. Testing showed the impracticalities of utilizing American aircraft at that time. Hoisting the tank hull under a C54 cargo plane and placing the turret in the plane proved cumbersome and time consuming. Because of the lack of a good air delivery system and disappointing performance of the vehicle, the Ordinance Department became less enthusiastic for any further development. However, the British were still interested in the vehicle and 260 were delivered with the remaining vehicles utilized for training purposes in the US. The British were more active than the US in airborne tank development having airborne tanks of their own such as the Tetrarch, Alexto and Hopkins. The British outfitted the 37mm guns with an extruder adapter (squeeze-bore) that reduced the projectile from 37mm to 30mm increasing velocity to 4000 ft/sec from 2700 ft/sec. A new high mass and shatter resistant tungsten carbide ammunition was developed for this application. Twelve of the tanks were landed using the giant Hamilcar glider during the Rhine crossing on March 24, 1945. The British airborne crossing of the Rhine river, called Operation Varsity, utilized over 50 large Hamilcar Gliders delivering airborne tanks and other equipment for the 6th Airborne Armored Reconnaissance Regiment, Royal Armored Corps, of the British forces. One Locust tank was credited with killing over 100 enemy soldiers.

ADDITIONAL TECHNICAL DATA