Pug had at first glance taken for junior lieutenants a couple of young men sporting the gilt collar leaves of lieutenant commanders.
Historically, the captain of small warships was usually a lieutenant commander (not an official captain).
A commissioned rank in the or Coast Guard that is above lieutenant junior grade and below lieutenant commander.
lieutenant commander
a commissioned naval officer who ranks above a lieutenant commander and below a captain.
A commissioned rank in the U.S. Navy or Coast Guard that is above lieutenant commander and below captain.
an officer holding a commissioned rank in the US Navy or Coast Guard; below lieutenant commander and above lieutenant junior grade.