The M22 Locust was a 7.4 ton light tank. It held a turret mounted 37mm cannon and a coaxial M1919A6 machinegun. It was developed by the US at the request of the British military, and used by the British near the end of WW2.
The T28 was a prototype super heavy tank with a 105mm main gun, and a .50 caliber machinegun on a ring mount. The tank was intended to be used to destroy heavy fixed defensive structures. Only two were ever built, and they never left the US. The project was stopped in 1947, but which time other heavy tank designs with comparable armament had been developed.
Not in the field?
Nah. That is just where they found it sleeping that day.