Ireland/Northern Ireland Timeline

[Sanjuro]

I also have some issues with PIRA being able to sink those minesweepers; firstly, mounting weapons that big on a motorboat is a lot more difficult than it sounds (British merchant vessels were only able to be armed during WW2 because they were legally required to have the mountings, and under-deck bracing, as part of British registry)- even a recoilless rifle is going to be difficult. Actually hitting the target would be very difficult- the lower Clyde and Firth of Clyde are rarely entirely calm, so keeping small motorboats stable enough for multiple shots would be very difficult. Probably the only practical weapons for the job would be the RPG7- and that means getting close, and being exposed to defending fire.
Secondly, as others have posted, the Clyde Naval base is defended by troops who are trained and prepared for Spetsnatz type attacks; small boats are one of the threats they expect.
Thirdly, the Clyde Boom would have been closed; sure, the boats could go through the Kyles of Bute and bypass the boom, but in wartime the Kyles would be unlit at night.
Finally, in wartime the Clyde's usual busy traffic of yachts and small craft is going to be greatly reduced, making the attackers much more visible.
In peacetime, the attack is barely feasible; in wartime, a suicide mission, with little prospect of success.