The T16 4.5in Gun Motor Carriage was a design for a self-propelled gun that was originally to be carried on a new chassis based on that of the M5 Light Tank, but that was then modified to use the M24 Light Tank chassis, before being cancelled.
Work on the T16 began in May 1941 when the intention was to mount a 4.5in gun on a chassis made from parts of the M3 Light Tank and parts of the newer T7 Light Tank.
The T16 was designed by Cadillac, the producers of the M5 Light Tank. It was developed at the same time as the T18 75mm Howitzer Carriage, T56 3in Gun Motor Carriage and T57 3in Gun Motor Carriage, all attempts to produce a self propelled gun using the standard M3/ M5 chassis. All three projects failed because the small light tank chassis simply didn't have enough space to carry the bigger guns.
Cadillac took a different approach to the problem. They produced a new chassis based on that of the M5, but lengthened by the addition of a third two-wheel bogie on each side of the vehicle. The engine was moved to the centre of the chassis from the rear, leaving space at the back for the gun compartment.
Two pilot models of the T16 were completed by the end of 1942, one with the 4.5in gun and one with a 155mm Howitzer and the new designation T64 155mm Howitzer Motor Carriage. They were tested at the Aberdeen Proving Ground and by the Artillery Test Board and performed well, but in April 1943 work began on a new light tank, the T24 (later to enter service as the M24 Chaffee). The new tank was being designed with alternative uses in mind, and the Artillery Test Board recommended that the T16 should be redesigned to use the new chassis. The T24-based version was given the designation T16E1, but the Armored Board then decided not to use the 4.5in gun and in February 1944 the T16 programme was cancelled.
The new M5 based chassis became the basis of a family of vehicles called the Light Combat Team. The idea was to simplify maintenance by using a common chassis for a variety of gun carriages. The extended M5 chassis was used as the basis for the T64 155mm Howitzer Motor Carriage, T65 40mm Gun Motor Carriage and T85 20mm Gun Motor Carriage. All of these projects moved onto the M24 chassis, becoming the T64E1 and T65E1. Of these projects the T64E1 entered production as the M41 Howitzer Motor Carriage and the T65E1 as the M19 Multiple Gun Motor Carriage.