The VGT128 argon filled thyratron is from the 1930s and was used in timebases for Radar. The fact that it is a UK Armed Forces badged GT1C is clear from the logo on the side.
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: Data-sheet, 1040 & 1043. Type VGT128 was first introduced in 1937. See also 1937 adverts.