First officers pulling double duty - exception or the rule?

[J.T.B.]

Then she wouldn't be called "Number One." That nickname is reserved exclusively for the XO, and has been throughout history.

It's a good point. But technically "Number One" was/is the Royal Navy nickname for the first lieutenant, who would be the second in command of a destroyer or smaller warship. On a battleship, cruiser or aircraft carrier, the second in command was "The Commander" and "Number One" was below him.

Roddenberry was in the US Army, he flew bombers.

He was in the US Army Air Corps which became the US Army Air Forces in 1941.

The Air Corps existed as a branch of the Army until the USAF was created in 1947, and it was common during the war for those serving in flying units to refer to themselves as belonging to the "Air Corps." But the Army Air Forces were also frequently called simply "the Air Force," which was technically not correct but wasn't discouraged by higher-ups who wanted it to be an independent service like the RAF. I find "USAAF" to be maybe the least confusing way to refer to the WW2 organization.

It wouldn't be impossible that the "original" first officer was killed and she was assigned to the position of first officer.

As first officer she still could have held the rank of Lieutenant, as first officer she wouldn't have to out rank everyone aboard the ship other than the captain (although I understand it helps), her position would give her authority over higher ranking officers.

Well, I suppose, but the real world military way to do it would be for the next most senior qualified officer to move up into the vacant position, nice and neat and nobody getting stepped over. All kinds of trouble happens when juniors are given authority over those of a senior grade.

 

[Nerys Myk]

He was in the US Army Air Corps which became the US Army Air Forces in 1941.

The Air Corps existed as a branch of the Army until the USAF was created in 1947, and it was common during the war for those serving in flying units to refer to themselves as belonging to the "Air Corps." But the Army Air Forces were also frequently called simply "the Air Force," which was technically not correct but wasn't discouraged by higher-ups who wanted it to be an independent service like the RAF. I find "USAAF" to be maybe the least confusing way to refer to the WW2 organization.

Yep. My Dad joined just before the USAF was created. He was a private for a short while until they introduced the airman ranks.

 

[T'Girl]

... as first officer she wouldn't have to out rank everyone aboard the ship other than the captain (although I understand it helps), her position would give her authority over higher ranking officers.

Well, I suppose, but the real world military way to do it would be for the next most senior qualified officer to move up into the vacant position ...

If the highest ranking officer below the captain was in a specialty, and the hypothetical Lieutenant was the next senior unrestricted line officer, then the position of first officer would go to that Lieutenant.

 

[J.T.B.]

If the highest ranking officer below the captain was in a specialty, and the hypothetical Lieutenant was the next senior unrestricted line officer, then the position of first officer would go to that Lieutenant.

OK, but the post referred to lieutenant Number One superseding a chief engineer who was a lieutenant commander. In Trek as well as the US Navy, engineers are line officers. It goes without saying that a qualified officer would take precedence over an unqualified officer of a higher grade.