Requirements for crew promotions in GWX?

[Annatar]

Just started a new career in GWX and have completed 5 patrols in my little Type II, only three of which were in war time. I think I amassed 4k tonnes in the third patrol, 2k in the fourth and 8k in the fifth, and although my Kaleun has been promoted, I've yet to recieve any for the crew.
I had the 'random crew' option from SH3 Commander enabled at the start of the career, but I'm not using SH3Cmmdr to update my crew between patrols, rather I'm letting the game do whatever it does normally.

Does anybody know the requirements to recieve crew promotions? I assume it's based on tonnage?

[Steeltrap]

I think it works via "experience".

Each crew member has two values - their experience and the value required to become eligible for the next rank (e.g. 207/250, meaning that person needs another 43 experience at least). They earn some experience each patrol, which may or may not be a function of each patrol's 'success'.

If you look at the officers at the highest rank, you'll see they have a current experience greater than the value for the next rank as they are at the maximum rank i.e. they can't get promoted, but keep gaining experience anyway.

Others with greater technical knowledge of how the mod might affect this can give the definitive statements on exactly how this works (if it differs from what I've said).