After some early evaluation, the T9 pilot vehicle was found to be lacking key areas. While sporting an-all welded hull and powered cast turret, it was too heavy for the intended role. Wheels were deemed too weak for the weight distribution required of the design and the expected rigors of combat use leading to the installation of steel beams to reinforce the suspension system. Armor protection was a long-term concern but the T9 pilot vehicle was already reaching its maximum allowable weight for use in the Hamilcar glider. As such, another form - the T9E1 - was developed with a new manually-powered turret (the intended gun stabilizer was dropped) and a revised, sloped hull design. A pair of .30 caliber machine guns fitted to the bow were now dropped to save weight. The suspension system was further revised to be made lighter and brought the T9E1 down to manageable levels for glider use.
Despite the fact that the T9E1 was more in line with the required specifications, the USOD had gone ahead and placed an order for production models following the T9 pilot vehicle standard in April of 1942 - the T9E1 pilot was not made available until November of 1942. Inevitable delays ensured serial production of the T9 was not forthcoming until April of 1943 (originally intended for November of 1942). In all, 830 M22 Locust Light Tanks were produced from the 1,900 that were envisioned and these were all based on the original T9 pilot vehicle. Deliveries ended in February of 1944 with the cancellation of its production line in favor of other wartime systems. It was the British, as with other American tanks, that bestowed the name of "Locust" to this American tank type.
As completed, the M22 Locust weighed in at approximately 16,400lbs (8 tons). She fielded a running length of just under 13 feet, held a width of 7 feet and a height of just 6 feet. Her standard operating crew consisted of the driver, tank commander and gunner. The driver maintained a position in the front left hull under a hinged door plate (usually left open during safe travel). The commander and gunner was positioned in the traversing turret with the armament. Of note is that the commander doubled as the main gun loader which only served to increase his workload and take his attention away from the unfolding combat situation. There were two methods of entry/exit for the crew - a hatch on the turret roof and a hatch at the driver's position. The turret - with full 360-degree traversal - was set at the middle of the short hull roof with the engine at the rear of the design. The engine exhausted to the right rear side of the hull, a pipe running from the rear center wall to the upper right track cover to which a muffler was affixed. Spare road wheels could be carried along the engine compartment roof. Ground clearance was rather small and the M22 promoted a very short, stout appearance. Her running tracks were relatively thin in comparison with medium tank designs but acceptable for the light tank role. The drive sprocket was held at the front with the track idler at the rear. Two track return rollers were fitted to guide the upper track portions. There were four road wheels to a track side, these attached as inline pairs. The M22 was powered by a single Lycoming O-435T series, 6-cylinder, gasoline-fueled radial engine developing 165 horsepower. This supplied the diminutive mount with a top road speed of 40 miles per hour and an operational range of 135 miles. The hull sat on a Vertical Volute Spring Suspension (VVSS) system to assist in cross-country travel.
As deliveries commenced, many were shipped for use by British airborne forces in Europe via Lend-Lease. For the Americans, the Locust would end up as nothing more than a training platform - resulting in just two experimental tank groups being formed and stocked with M22s (the 28th and the 151st Airborne Tank Battalions). The Americans lacked any sort of indigenous glider capable of transporting the M22 (like the British Hamilcar) and could only utilize their Douglas C-54 transports to move them. Even then, the M22 would have to have its turret completely removed to make her fit in the hold and their hulls were left exposed under the aircraft. As such, the system held very little inherent benefit to the US Army and its airborne forces.
It is believed that very few M22s ever actually saw combat service when used - and these being utilized primarily by the British airborne. In fact, less than a dozen are thought to have been used in an operational combat manner, leaving the rest for either training or reserve roles until the end of the war. The most notable use of the M22 was in the crossing of the Rhine River in 1945 at Wesel through "Operation Varsity", these elements as part of the British 6th Airborne Division. For US airborne troops, the M22 was never to see combat in the whole of the war. In January of 1946, the M22 was officially classified as obsolete, formally bringing about her end with American and British forces.
M22s suffered a myriad of issues uncovered largely during its evaluation. As a light tank, she was thinly armored by mid-war standards and could easily be knocked out by the smallest-caliber anti-tank weapons and wholly decimated by large-caliber tank guns. Even small arms fire could penetrate its armor at key points, rendering the system highly vulnerable. The 37mm main gun was also insufficient to combat the expected enemy tanks at this point in the war. The powertrain was underpowered for the design's weight and reliability proved an ongoing concern in-the-field. Despite its specifically-design use in conjunction with the Hamilcar glider, tests showed these loading/unloading times to be exceptionally long, exposing the handlers to the hazards of the battlefield for prolonged and unacceptable periods. If the M22 held any advantages it was in her inherent speed - other than that, she had very little to recommend herself at this late stage of the war. Some British M22s had "Littlejohn Adapter" systems affixed to their 37mm main guns to help assist in its penetrative capabilities but these ultimately held little bearing.
Post-war Locusts existed in a few modified forms. The British passed on some of their M22 inventory to the Belgians while scrapping the rest in reserve. In Belgian Army service, they were modified as command tanks - sans their turrets and armament - to work in conjunction with their M4 Shermans Medium Tanks. Egypt became another post-war user of the light tank type, fielding the M22 against Israel in the 1948 Arab Israeli War. Captured systems were then put back into limited service by the Israeli Army for a time, even seeing action in the 1956 campaign across the Sinai Peninsula. In Egyptian service, the M22 was eventually superseded by the influx of Soviet hardware throughout the Cold War.