Oh dear, I have made a big boo-boo.

Jack Smith is the next name down from Alec and I copied and searched the wrong number!! I'm very sorry. Alec Smith's number was 1675139/165806
1675156 Jack SMITH (Commissioned number: 165753). Commissioned at the same time as Alec.
Promoted to Flying Officer in 14 Jan 1945.
And Navigator was a role rather than a rank. They were, as the word implies, navigated the aircraft to and back from their target. However, without his record it would be impossible to say which type of aircraft he was on.
Must stay off the eggnog
K