name='maturin']For Those In Peril
has a lot of small boat action, including an MGB, and there's a bit at the start of The Ship That Died of Shame
of course but that's MTB vs. gasworks.
If it's a documentary, could it be The Broad Fourteens
"A dramatised account of the first posting, and eventual first action, of a newly-trained motor torpedo boat (MT
crew. ('The Broad Fourteens' is the name given to an area of the North Sea off the Dutch coast.)
The film joins the boat and crew at the end of their training (probably «HMS Bee», the Coastal Force working up base at Weymouth). The Training Commander offers last words of advice to the Commanding RNVR Lieutenant. «MTB 181» sails to join a North Sea operational base («HMS Terrier»). Despite the crew's enthusiasm, however, their first several operational sorties bring them no action (but film of the men excited, disgruntled, relaxing etc. develops "characters" for the purposes of the plot). Eventually, the flotilla is briefed for an attack on "the best target you've had for several weeks", a convoy on the Dutch coast. In the ensuing action, «MTB 181» sinks the tail escort (a flak trawler) with torpedoes, but then runs foul of two S-boats; one is disposed of by dropping depth charges in its path, but the MTB suffers damage and casualties, and as the second S-boat closes in is saved by the return of the rest of the flotilla."