I was a submariner stationed in Holy Loch one summer - the last summer, of 1991 - aboard the USS Ulysses S. Grant. I returned once, in the winter of 1999. I have not seen this movie, but will as soon as I can now that I know about the subject matter.
Dunoon is something of an exception to the rule on Scottish hospitality. Many Dunoon Scots did not like Americans, it's true. Maybe it had something to do with the low-browed, hard-drinking and pugnacious attitude of many of the working class Americans who join the Navy. Then again, low-browed, hard-drinking, pugnacious and working class describes many Scots from Dunoon. It might have also had to do with some latent racism towards African-American sailors, or with the fact that many US sailors competed with Scots for the affections of the local women - as I understand this movie depicts. However, I think it had mostly to do with the left leaning politics of the area and an underlying inferiority complex. Dunoon Scots, to the extent they did, disliked Americans for the same reason Frenchmen do. Oh the irony that they so lamented the US Navy's departure in 1992. They seem to like Americans even less now, as I discovered when I tried to find a room last minute in 1999. The Scots in nearby Oban and Inveraray, however, seem to hold no such prejudices.
I must say that there were also those in Dunoon who were very hospitable, and I never had trouble finding a good place to have a friendly pint of Tennent's Lager or McEwan's Ale, or a bite of fish 'n' chips after the pubs closed, before I stumbled back in the dark past St. Cuthbert's Kirk on the long walk to the ferry in Sandbank.
In any case, I loved Dunoon and the surrounding Cowal, Argyll & Bute. The land is fairytale magical in the summer, like something out of the Lord of the Rings movies. In winter it is magical as well, but in a less than fairytale way.
Reading the synopsis, I would point out a fundamental flaw in the movie. Unless I missed something, there was no shore patrol in Dunoon, and I don't remember ever seeing a US Marine.