rotating orange light

[MarieK]

I would imagine its linked to the Bilge alarm to alert passers by or other marina users that there is a problem. A lot of the trawlers in my home port have them so if somebody working at the harbour sees a flashing light they can alert the owner.

 

[maxi77]

So why does a sub have to identify itself as such, and not just act, and be lit as any motor vessel?

I think it came from the Yanks who always had a yellow grimes light on their boats coming out of the Holy Loch and I expect other bases too. One of the reasons is submarines are not well endowed with good places to fit navigation lights so the grimes light helps make people look twice at the strange positiong of the lights with espect to the overall size of the hull. Equally when you think of the black losheen painted hull and the absence of any deck lights some help for the normal mortal may be seen as a good thing.

Mind you a chum of mine was obliged to inform his captain on an O boat progressing up the Clyde through the Cumbrae Gap that the USN SSBN that had previously been reported had just turned right over the hill on Bute.