The R type triode was conceived 1915 in England, based on the French TM type triode. This and the TM type were the first commercially produced hard vacuum valves. 100,000 of each of the R and the TM types were made during the Great War, for allied radio receivers. The first R type had a horizontal electrode axis and a crucifix base with 4 bifurcated pins, and a bright emitter filament of pure tungsten. This example of the R type was made after 1921. It has a vertical electrode axis and a 4 pin UV base with equi-spaced stubby hollow pins. It requires a skirted socket with a slot for the locating pin on the side of the valve skirt. The silvering on the glass is an internal metal getter to mop up residual gases. It has a dull emitter filament coated with oxides, operating at a lower temperature than tungsten.