The GT1C thyratron is from the late 1930s and was used in timebases for Radar. This exhibit is branded as made by Marconi the GT1C held at HMS Collingwood in the John Lawrence Collection is branded GEC. GEC owned the production facilities that made both valves and normally industrial valves carried the GEC logo.
At a defined grid voltage a Thyratron 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 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 42 mm in diameter and, excluding the B5 base pins, is 100 mm tall.
References: Datasheet, 1040 & 1043. Type GT1C was first introduced in 1937.