Injection of solid tritium pellets is considered to be the most promising way of fueling fusion reactors. The Tritium Proof-of-Principle experiment has demonstrated the feasibility of forming and accelerating tritium pellets. This injector is based on the pneumatic pipe-gun concept, in which pellets are formed in situ in the barrel and accelerated with high-pressure gas. This injector is ideal for tritium service because there are no moving parts inside the gun and because no excess tritium is required in the pellet production process. Removal of 3He from tritium to prevent blocking of the cryopumping action by the noncondensible gas has been demonstrated with a cryogenic separator. Pellet velocities of 1280 m/s have been achieved for 4-mm-diam × 4-mm-long cylindrical tritium pellets with hydrogen propellant at 6.96 MPa (1000 psi).