Not true at all...
In the Navy, the person in command of a ship is referred to as “Captain,” no matter what his actual rank.
I seem to recall seeing a Lt Commander who was in charge of a ship, and another Commander who was in charge of a submarine.
Both were correctly referred to as “captain!”
Mark
Yep. Most submarine captains are, in fact, Commanders. I even saw a Master Chief Captain on a tug once.