Rather than providing the history of the Tank Destroyer Forces as a narrative, I felt it would require a lot less reading, and be easier to find specific dates, if it was done in time-line form.
Feb. 2, 1942.....Project started to mount 90mm gun on an M4 tank chassis, designated as the T53
Sep. 3, 1942.....T67 with 75mm gun tested
December 1942.....Modified 90mm designated T7 was completed and mounted in a pilot M10. Result designated the T71
Jan. 1, 1943.....McNair directs TD Center to conduct tests of towed TDs
Jan. 7, 1943.....1000, T70 Gun Motor Carriage (GMC) w/76mm gun, torsion bar suspension and twin diesel engines ordered
Mar. 3, 1943.....Chevrolet began development of a balanced turret for the T71
Mar. 12, 1943.....Tentative T/O & E for towed guns completed. Ratified on May 7, 1943 and published as FM18-35
July 1943.....Pilot T70s delivered & tested, resulting in 157 major modifications
September 1943.....Ford shipped completed T71s to Aberdeen, MD, for testing. They had mild steel turrets, Ford V8 engines and were mounted to the M10A1 chassis
Feb. 17, 1944.....T70 was standardized as the M18 GMC. They were nicknamed the "Hellcat"
April 1944.....Limited production of 500 ordered and started of the 90mm GMC M36 by Fisher, completed in July
October 1944.....Production of the M18 is halted. A total of 2507 were manufactured