Exercise "BLANKET"

Whilst looking for something else, I came across in the Admiralty War Diaries a signal about Exercise BLANKET on 29.10.1942. This had six small boats testing whether they could penetrate the Thames defences. They used the "dark night period" with camouflaged boats carrying two men and using paddle or sail propulsion.

I wonder if this was a dummy run for one of the raids on the Continent or checking whether British defences would detect a similar German attack?

I have been told elsewhere that it was a practice for Operation FRANKTON by a small unit from the Royal Marines Boom Patrol Detachment.