The VU39 is a pre-CV register name for a full wave rectifier used by the RAF. This valve when used by the UK Government was labeled VU39 for the RAF or NU17 for the Navy or AU3A for the Army or even the POVT142 when purchased by the GPO. The rationalisation of the 1941 CV (Common Valve) register called the specification the CV1039.
The specification was based on rectifiers from the major manufacturers:- MU12/14 from M-OV, UU5 from Mazda, IW4 from Mullard etc.
The anode sections are mounted high in the envelope and clearly a much smaller tubular envelope could have been used.
The blackened anodes are pressed with ridges to give structural rigidity.
The classic envelope is 45 mm in diameter and excluding the B4 base pins, is 101 mm tall.