MILITARY VESSEL visitation

[Oldhands mike]

Hi to one and all
I have a need to satisfy a very old instance- at some point in the early sixties,as a child I use to be taken to the swings on the West hill to have a go and play, however on one day,we crossed the road and whilst walking towards what would be the CAVES entrance direction I seem to recall seeing what was a large light grey naval boat moored off shore- between the harbour arm and the castle rocks,my recollection at such a tender age,was that is was HUGE.It was not moored off the end of the pier as some visitations were,it was not a submarine and not a fishery protection vessel.The only thing I'm certain is the time period of the 1960's.
Any body out there that could throw some light on this subject ??

[whiffler]

Maybe for 1966 battle anniversary ?