The Type 10 tube is a filamentary triode tube with a filament voltage of 7.5 volts and filament current of 1.25 Amps.  It has a standard UX4 base 4 pin base.  It is typically used as an audio amplifier tube.  Max Plate voltage is 425 Volts and Max Plate Dissipation is 12 Watts.  

The US Military designation is VT-25.  There were two types of filaments used with 10's.  Most common is the Thoriated Tungsten variety which have short plates and glow quite brightly when the filament is activated.  There was also a coated filament variety which had "long" plates.  These were called VT-25A's  Contrary to popular belief, these DON'T have a higher power rating.  Early 10's were in the "globe" shaped envelope (S) and later ones were fitted with the "ST" shaped envelope.  There were 2 different sized ST envelopes used.  (small & large)