This icon and two in-game picture were supertest leaks.
It would have been between the T82 and T40 but was droped to let the tanks stemming from the T40 to drop a tier; so it is unknown if it will be introduced in the game.
The in-game description was also leaked: Experimental self-propelled gun on the M3 chassis. The Baldwin Locomotive Works Company started the development of the T24 in the fall of 1941. By November, the prototype was completed. The vehicle passed trials, but never saw mass production.