Commander Lee Crane never got promoted

Okay, for those with no knowledge of military ranks, "captain" Lee Crane of the super nuclear submarine, Seaview, had an actual military rank of, O-5, which in the U.S. Navy is, commander. Now, whenever a navy commissioned officer commands any vessel, on the ocean or below it, his "title" is, "captain", as in, captain of the ship. His actual military rank could be as low as, O-3 which is, 'lieutenant' in the navy.

The good captain Crane remained in the commissioned officer rank of, O-5, that is, Commander, for the entire series. He never got promoted to O-6, which is officially titled, Captain. There was an episode in which captain Crane meets up with another advanced U.S. submarine, captained by an O-6, which you could tell by the eagle insignia on the man's collar. Captain Crane wore silver oak leaves on his collar lapel. Both men in the episode got into an argument but the O-6 never tried to pull rank on Crane, and Crane was never intimidated by the man's higher rank. This was because both men were addressing each other as fellow sub captains, which made them equal, in Navy culture. Now had both men been assigned to land duties in some office, then the O-6 could have pulled rank on Crane and forced him to back down.
I would have liked to have seen Crane promoted even to one-star admiral. It's not beyond belief that he could have captained such a huge and highly advanced submarine as a one-star admiral, whereas all ships and subs are captained by men in the ranks of O-5 and O-6 for the major vessels, smaller ones being captained by O-4 and even O-3. But then again, you couldn't have two admirals on the same vessel. Crane would be without his four-star admiral mentor.