The GT1C thyratron is from the 1930s and was used in timebases.
At a defined grid voltage the valve will rapidly switch to full conduction. The valve is turned off by reducing the anode voltage. This valve not only has a high peak current but is designed for operation at up to 8,000 pulses per second.
This GT1C carries the Osram label. Within M-OV GEC was used for professional devices and Marconi and Osram were for consumer products. This is the first example seen with the Osram label.
The classic envelope is 44 mm in diameter and, excluding the B5 base pins, is 101 mm tall.
References: Datasheet, 1040 & 1043. Type GT1C was first introduced in 1937.