The Lieutenant is a member of the United States Air Force. His real name is unrevealed, but he serves as an adjutant under a similarly unnamed Colonel on a secret military experimental project that produced and tested the XJP Jet Pack. Unfortunately, he has the unpleasant task of delivering the news that the jet pack has been lost overseas while the project's supervisor, an unnamed general is present. He later receives the order to have it recovered, unaware it has washed up on the island with the castaways of the S.S. Minnow.
- The Lieutenant was played by actor Walt Hazzard.