The GT1C thyratron is from the 1930s and was used in timebases for Radar. Thyratron was a trade name for a gas filled triode. In the case of the GT1C the low pressure gas was Argon.
At a defined grid voltage, the valve will rapidly switch to full conduction. The valve is turned off by reducing the anode voltage. Thyratrons are gas filled and can be considered as triggered gas discharges. The precision of construction gives the defined and reproducible operating characteristics. This valve not only has a high peak current but is designed for operation at up to 8,000 pulses per second.
The GT1 had similar ratings and had a mercury vapour filling.
The worlds first computer, Colossus, used these thyratrons as pulse generators. The operating speed of Colossus was 5,000 cycles per second.
The classic envelope is 46 mm in diameter and, excluding the B5 base pins, is 104 mm tall.
References: Datasheet, 1040 & 1043. Type GT1C was first introduced in 1937.