The VGT128 argon filled thyratron is from the 1930s and was used in timebases etc. This valve was made for the Government controlled General Post Office that ran the telephone system and various government communications.
The worlds first computer, Colossus, used these thyratrons as pulse generators. The operating speed of Colossus was 5,000 cycles per second.
The Type designation is etched into the glass as well as the printed version with the old stores code seen above. The shape of the etched ellipse is typical M-OV.
The shielded anode is on the left with the copper supports for the grid or trigger just over half way to the right of the image. The indirectly heated cathode is on the right. The outer cylinder is a screen connected to the cathode.
The original box with basic instructions.
The classic envelope is 45 mm in diameter, and excluding the B5 base pins, is 103 mm tall.
References: Data-sheet, 1040 & 1043. Type VGT128 was first introduced in 1937. See also 1937 adverts.