The VR54 is a double diode with the VR indicating a receiving valve for the UK Royal Air Force. The specification was based on the commercial EB34 and function would be in signal detection etc..
The diodes are rated for signal use, with separate cathodes and a screen between sections.
The reverse has 6H6 printed on it. The two valves are pin compatible. The 6H6 heater is rated at 300 mA whereas the VR54 is rated at 200 mA. The maximum anode voltage of the 6H6 is 150 V and the VR54 can be as high as 200 V. So the VR54 can replace the 6H6 but one has to be careful in replacing the VR54 with the older 6H6.
Seen from the top: two small cathode tubes and a central screen.
The wide glass tube envelope is 28 mm in diameter and, excluding the IO base pins, is 62 mm tall.
References: Data-sheet & 1040. Type VR54 was first introduced in 1941.