World War 1 (1914-1918) had proven the validity of the "tank" as a requisite of future battlefields so the United States Army, heavily reliant on foreign designs during the conflict, persisted in developing homegrown solutions in the post-war period. This commitment went hand-in-hand with the emergence of J. Walter Christie, an automobile design who would eventually lend his name, and find global fame, to the "Christie Suspension System".
From 1918 into 1919, Christie interested the United States Army's Ordnance Department in several of his designs for "Gun Motor Carriages" but none were adopted. Regardless, these projects allowed Christie to fine tune a suspension system known as the "Convertible Suspension" which allowed a heavy vehicle to operate on either roadwheels or linked track sections. This hybrid arrangement was of note for the period when tanks proved so unreliable that they were shuttled to the front on the back of trucks so as to save them on wear and tear and reduce the change of mechanical malfunctions. The Christie method would allow a vehicle to take to the roads, at speed, utilizing a proven car/truck like function. Once at the front, the tracks could be applied and the usual bogies would come into play.
Christie netted an Army contract in November of 1919 through his Front Drive Motor Company to produce a new combat vehicle utilizing the convertible suspension system. He then returned with his design for the Model 1919 (M1919) tank in February of the following year.
The M1919 Christie Medium Tank was arranged as planned. Four large roadwheels were set at the extreme corners of the tank's hull. Between the axles, along the center section of the hull sides, was a single bogie managing a pair of small roadwheels. Drive power was from the rear-mounted axle and a linked-track section was applied over all the wheels when the vehicle was readied at the front. The hull consisted of a boxy structure which supported a rounded turret housing the American-equivalent of the British 6-pounder gun, the 2.24" (57mm) M1920. Over this structure was a smaller, half-sphere enclosure fitting a 0.30 caliber machine gun. Since the turrets could turn independently of each other, the tank could engage two targets at once.
Power was from an in-house Christie 6-cylinder water-cooled gasoline engine outputting 120 horsepower. Maximum speed was 13 miles per hour on roads when using the road wheel configuration and 7mph when the vehicle ran on the tracks.
The crew numbered three and the vehicle sported a length of 18.1 feet, a width of 8.5 feet and a height of 8.8 feet. Overall weight was 13.5 tons and armor protection measured 0.25" to 1" at the various facings.
The famous Aberdeen Proving Ground (Maryland) was the site of the vehicle's testing phase. Observers were quick to criticize the vehicle's lack of suspension which made for a very bumpy ride on the rigidly mounted wheel sets. Also cross-country performance on the tracks showcased a tank that was much too underpowered for the new mechanized formations being planned by the Army. Further trials failed to convince Army authorities to pursue the vehicle further which led Christie to convince the Army to postpone judgment - and additional testing - until he could revise the design some.
After almost a year (1922), Christie returned with the reworked attempt which added springs to the front wheel members and deleted the turret altogether. The armament was now in a box-mounted barbette offering limited firing arcs. This offering, the M1921, managed to improve performance and comfort some but the Army still deemed the vehicle unreliable and underpowered, leading to an abandonment of this Christie attempt. The M1921 was tested up until July 1924 before being given up for good.