The title ( originally `` master and commander '' ) originated in the 18th century to describe naval officers who commanded ships of war too large to be commanded by a Lieutenant but too small to warrant the assignment of a post-captain and ( before about 1770 ) a sailing-master ; the commanding officer served as his own Master .
The title ( originally `` Master and Commander '' ) originated in the 18th century Royal Navy for naval officers who commanded ships of war too large to be commanded by a Lieutenant but too small to warrant the assignment of a Post-captain .