J. Walter Christie turned his considerable skills in engineering toward military tracked vehicles and came up with the M1919. Both turrets on the M1919 could turn 360 degrees. Tested at Aberdeen Proving Grounds, it turned into a disappointment for Christie and he asked testing to be halted. Christie returned again with the M1921, though rejected, it was a bit of an improvement. Both tanks could run on either track or wheel and was a true engineering marvels for their time.