The favorable performance of an eight wheel (8×8) vehicle developed by the Cook Brothers of Los Angeles, California resulted in a design study to adapt the chassis as a 3 inch gun motor carriage. The design utilized the 3 inch gun mount M4 developed for the 3 inch gun motor carriage M5. The new vehicle was designated as the 3 inch gun motor carriage T55 and was popularly known as the “Cook Interceptor”. As originally proposed, the vehicle had two engines, one in front and one in the rear, with each engine driving one four wheel bogie. In the final design, both engines were installed at the rear. Steering was with the aid of a hydraulic booster and was accomplished by turning the entire front bogie about a center pivot point. Two pilots were constructed with the second somewhat modified in design. The latter could be readily identified by the angular shape of the hull compared to the curved hull design of the original T55. The second pilot was designated as the 3 inch gun motor carriage T55El. Tests at Aberdeen Proving Ground revealed that the cross-country mobility of the Cook vehicle was inferior to that of a full track tank destroyer such as the T49 then under test. Both the T55 and the T55E1 were canceled without further production.
Earlier wheeled carriages for the 3 inch gun had been considered. The first was the previously mentioned T7 which was a modified version of the armored car T13. The second was the 3 inch gun motor carriage TIS which proposed to mount a 3 inch gun on a special Ford, four wheel drive, chassis. Later plans changed the special Ford chassis to a six wheel drive version. However, the project was dropped completely in October 1941 and the two T55 series vehicles were the only wheeled 3 inch gun motor carriages actually constructed.