A hydrogen fuel vaporiser (218) is shown for vaporising cryogenically-stored hydrogen fuel prior to injection into a gas turbine engine. The vaporiser (218) comprises a fuel offtake (301) configured and arranged to divert a portion of hydrogen fuel from a main fuel conduit (217), a burner (303) configured and arranged to burn the portion of hydrogen fuel diverted from the main fuel conduit (217), and a heat exchanger configured and arranged to transfer heat produced by the burner to hydrogen fuel in the main fuel conduit (217).