The M9 was a similar model to the M2 but was based on the M5 Half Track and was designed as a gun tractor for the US version of the 6pdr A/T gun.
It had the same size body as the M5 and had stowage lockers in the side.
They were supplied to the British Army.

This conversion is designed for the PSC M3 H/Track kit but may fit other makes with some modifications.
The Half Track at Bovington tank museum is an M9.