The UK Navy valve NR75 is based on the commercial AC/P4 from Mazda. It was designed as a television line output valve.
Some of the stores label remains. The valve also carries the wording pair No. 1007. Radiomuseum says that NR75 was a matched pair of triodes in a single package. Given that the valve is a single triode this must relate to the fact that a pair were matched at the factory and supplied in a box together. Thus the line output stage was to have been a triode push-pull pair.
The carbonised anode is much wider than the from to back dimension. It is 28 mm wide, 22 mm tall and 4 mm front to back.
The top of the anode showing the flat coated cathode and grid wires.
One side of the grid cooling fin.
The classic envelope is 39 mm in diameter, and excluding the B5 base pins is 110 mm tall.
References: Datasheet, 3002 & 1043. Type NR75 was first introduced in 1939.