The 1H5GT is a dry battery diode triode for receiver use. The 1LH4 is the same valve but on a B8B base. In a TRF receiver the diode would provide AM signal demodulation and the high μ triode would be the first audio voltage amplifier.
Normally the Glass Tubular (GT) valves are made as short as practical and our Sylvania 1H5GT is 15 mm shorter.
The Mullard name and the word Amerty. Amerty indicates a valve made in America for Mullard.
The octagonal border to the Type designation looks like an RCA made valve.
The single strand filament drops through the triode into the screening box that contains the rod anode of the diode.
The wide glass tube envelope is 30 mm in diameter, and excluding the IO base pins is 86 mm tall.
References: Data-sheet, 1040 & 1043. Type 1H5GT was first introduced in 1940.