Moorhead VT-B with British B4 base cap. This was also known as the Type B transmitter. Most, if not all, were made for the British military.
Thanks to Joe Gruber for sending the images.
The balloon envelope is mm in diameter and, excluding the UV base pins, is mm tall.
Reference: Joe Gruber. Type VT-B was first introduced in 1917.
Updated October 04, 2020. shape:balloon construction:pinch type:triode age:pre.1920 base:uv pins:4 pin:1.g1 pin:2.f pin:3.f pin:4.a