Defiant may refer to any of the following Manticoran naval vessels:
- MSNS Defiant, a frigate of the old Manticore System Navy.
- HMS Defiant, a ship in Edward Saganami's anti-piracy force.
- HMS Defiant, a battlecruiser and the flagship of Commodore Prentis.
- HMS Defiant, a light cruiser and Captain Aivars Terekhov's command in the Battle of Hyacinth.