This valve is an unusual variant of the disc seal triode. The type designation is military in origin. The overall apparatus consists of the valve and an external cavity.
The gap between the grid mesh and the flat end of the shaped copper anode can clearly be seen.
In this picture the close spaced gold coloured mesh grid can be seen as well as the shape of the external anode.
The co-axial envelope is 40 mm in diameter at its widest, and overall it is 72 mm tall.
Updated January 18, 2013.