The VT-109 (2051 commercial) thyratron is a gas filled tetrode for pulse generation and/or timing circuits. The data-sheet shows that by 1944 it was for replacement use only.
The side view.
The RCA logo on the base. Above the pinch, the twisted heater and cathode is on the right and the glass sheathed anode lead is on the left. The control electrode is in the centre.
The classic envelope is 37 mm in diameter, and excluding the IO base pins is 89 mm tall.
