The VT45 is a battery RF triode with a 3.5 Watt anode dissipation and a working frequency up to 20 MHz. The prototype was the M-OV X56. The later CV code was CV1045.
The base shell is ceramic and this has a lower loss at RF at high humidity. VT is the RAF code and this was very likely used in an aircraft transmitter.
The lozenge etched into the glass is typical of M-OV.
Inside the bright anode the four vertical filament strands can be seen.
The top micas with filament tension springs at the top level.
Through the hole in the top mica the grid wire and one filament can clearly be seen.
The classic envelope is 45 mm in diameter, and excluding the B4 base pins is 91 mm tall.