In the United States the National Defense Act of 1920 downsized the army to 280,000 officers and men. Amendments to that act abolished the Tank Corps and relegated tanks and their development to the infantry. In most nations, tank advocates found themselves marginalized; career officers interested in armor were encouraged to go elsewhere. Thus Lieutenant Colonel Dwight D. Eisenhower and Major George S. Patton Jr., disparaging of a future with tanks, reluctantly transferred to other military branches. Not until 1931 did the U.S. Army cavalry, which still employed horses, receive light “tankettes,” known as “combat cars.”
Such tankettes, which were built by all the major armies, were small, largely unsophisticated, easily manufactured, and inexpensive AFVs. These lightly armed and armored tanks manned by two-man crews became the basis for subsequent weapons carriers and light tanks. One of these, the British Vickers 6-Ton series, led to the Polish 7 TP of 1932 and the Soviet T-26A tank of World War II. It also influenced design of the U.S. Light Tank T1, the prototype for the M1–M3 light tank series.
The United States produced few tanks during the interwar years. Those developed were intended for infantry support, because the National Defense Act of 1920 had made tanks an infantry responsibility. The U.S. Army General Staff had decreed that the role of the tank in war was “to facilitate the uninterrupted advance of riflemen in the attack.”
Tanks were to be of two types: light and medium. Light tanks were to weigh no more than 5 tons so that they could be transported by truck; the mediums were to be no more than 15 tons to meet bridging requirements. Tank development in the United States was severely hampered by budgets in the 1920s, which allowed production of only two experimental models per year.
Influenced by the British, in 1927 the General Staff set up the small experimental Mechanized Force of light tanks, but in 1931 Chief of Staff General Douglas MacArthur decreed that tanks would have an exploitation role apart from infantry support, and the cavalry took over the Mechanized Force. In order to get around the National Defense Act, cavalry tanks were designated as “combat cars.”
The Light Tank T1E1 of 1929 was an unsuccessful design, although its sprocket drive and rear engine were both adapted in later models. Then in 1931 the United States purchased a Vickers 6-Ton Model B and used it as the basis for the four-man T1E4 of the same date. At some 17,200 pounds, the T1E4 had a 150-hp engine, a top speed of 20 mph, and maximum 16mm armor protection. It was armed with a 37mm main gun and single machine gun. It also had the two features (a rear engine and sprocket drive) adopted in subsequent U.S. light tanks.
The United States did not lack capable tank designers, and the most brilliant of these was certainly John Walter Christie of Hoboken, New Jersey. Christie produced a large number of revolutionary prototypes that had worldwide impact. During World War I he had designed several tracked gun carriers, one of which was a wheel-and-track carriage for an 8-inch gun. This experience led Christie to design the first U.S. postwar tank, the three-man, 30,200-pound Medium Tank M1919. Manufactured by Christie’s Front Drive Motor Company, and popularly known as the Christie M1919, the new tank resembled the Renault light tank in external appearance but incorporated important new design features, including sloped armor.
The steel track links of the early tanks soon destroyed less durable roads, so Christie’s M1919 was designed to run on interchangeable tracks or wheels. It featured sloped armor and center bogies that could be raised to allow the tank to run on its wheels. The tank crew could remove the track in about 15 minutes and store it around the tank hull during road operations. It also had the same speed in either forward or reverse and a superior power plant and suspension system.
Christie’s design immediately increased power, speed, and range, but it was also plagued by mechanical problems. The Christie M1919 had a 120-hp engine, a top speed of 7 mph, a three-man crew, and maximum 25mm armor. It was armed with a 57mm main gun and one machine gun. Christie had no shortage of designs. His Amphibious Gun of 1921 was a 75mm gun carrier that had its sides packed with cork to increase flotation. It led to the first amphibious tank. Another had sets of wheels to the front and rear of the tank hull that could be lowered to permit it to run without the treads.
In 1928 Christie introduced his “National Defense Machine,” the M1928, often referred to as the M1940, because it was regarded a decade in advance as far as tank technology was concerned. The M1928 was indeed a breakthrough in tank design. Powered by a Liberty aircraft engine, it incorporated a practical drive system with chain link from sprocket wheel to rear bogie. It also had a revolutionary suspension system of large weight-bearing wheels on torsion bars. Each solid rubber–tired bogie wheel was located at the end of a crank, pivoted in the hull and sprung by a vertical coiled spring. This enhanced the tank’s stability as a firing platform as well as its speed, potentially increasing the tactical and operational mobility of armored fighting vehicles in general. Army Chief of Staff General Charles Summerall, who supported the development of light tanks, was so impressed with the M1928 that he circumvented the Ordnance Board and ordered the Infantry Tank Board to test it.