Yes it was a very busy time. There was a Blue Funnel Priam class vessel fitting out just down the river. My next drydock in the area was on the Armadale in the early seventies and the there was a lot going on then.
I was an apprentice on the Denby Grange at the time of the alleged sinking. The patrol boat was, in fact, no more than a small open boat with a machine gun that got swamped by our wake. We didn't give it much thought at the time although my parents told me later that it made the national news. My pay doubled to an amazing twenty seven pounds a month while we were in the war zone.
Just saw this pic and the design of the midships accommodation made me think of a Shell H boat, then I had another look which made me think otherwise.
However, a British tanker built in 1958 with bridge wing cabs? Now that is unusual!
This ship (cunningly renamed "Derby Grange" is the subject of an excellent book entitled "On the Bridge - The King Billy Story" by Bill George, the Bosun. King Billy, refers to the Master whose character and leadership are the main subjects of the book, which gives a detailed, sometime hugely funny account of an 11 month voyage in 1966. Published by Seaman Publications. Highly recommended. I would be interested if any members of the crew of the voyage in question are members of SN.