The 2051 thyratron is a gas filled tetrode for pulse generation and/or timing circuits. The datasheet shows that by 1944 it was for replacement use only.
The box appears to be the second grid, seen with top and bottom micas. The heater connection can be seen on the left underside. To the right the anode lead is sheathed in glass from the pinch to the inside of the shield. The American military classification as VT-109 is also clearly seen making it identical to the commercial device.
The wire to the left of the bottom mica is the cathode. The wire passing down from the pinch held the getter.
The main connections: the control grid is the central plate.
The classic envelope is 38 mm in diameter, and excluding the IO base pins is 86 mm tall.