Sinking of the Laconia

Anybody else watch it on BBC2 ?
Not too bad a programme I suppose,but a little lacking in crew personalities perhaps,the U boat captain came over quite well.
But i was a little amused by the uniform that Mortimer was wearing,he was supposed to be a junior third officer – but his uniform had what appeared to be a
naval badge on his arm and he had (three ?) inverted chevrons on his epaulettes/shoulders.I would have thought that a 3rd officer would have had a thin stripe (lace) with either a full or half ‘curl’ on top !.
But then again I am not an expert on old cunard rank insignia ! anybody any ideas ?