The UK Army ARP18 is an output beam tetrode with the specification based on the commercial KT24. The old RAF code is VT51 and the Type designation became CV1334 with the unification of UK Government specification and procurement with the CV register.
This low power output valve has a bright anode. The filament tension springs are mounted on a top mica sheet.
The feint etched lettering gives M-OV as the maker and the brand is the professional GEC. Inside the anode the two wire grids can be seen but the image has been optimised for the lettering.
The top mica hold the tensioning springs the lower mica has fingers to grip the inside of the envelope and hold the electrode assembly rigid.