John Wingate, Below the Horizon, 1974
Iceland
ICGV Hekla
Offshore Patrol Vessel
Length: 204ft
Speed: 19 knots
Armament: 1 x 57mm gun
Note: This ship appears to be based on the ICGV Óðinn, a Icelandic Coast Guard vessel that had a prominent role in the second and third Cod Wars.
ICGV Laki
Length: 187ft
Speed: 18 knots
Armament: 1 x 57mm Gun
No other details provided
ICGV Stóri
Length: 206ft
Speed: 17 knots
Armament: 1 x 57mm gun
No other details provided
Note: I do not have a good source on the Icelandic Coast Guard, it is possible that the last two ships are real, but I've been unable to confirm this.
Plot summary: As the third Cod War drags on, the tension increases leading to fears of a Third World War...
Note: The 'Cod Wars' were a series of confrontations between Iceland and Great Britain over fishing rights in the North Sea, Iceland ultimately prevailed by threatening to leave NATO. What the author does in this novel is a fairly straightforward extrapolation of what was going on at the time with a few minor tweaks.
I became aware of this novel when the author mentioned it in a footnote to his later submarine disaster novel 'The Sea Above Them' (1975), indicating the two stories were set in the same fictional 'universe'. That reference implied this story was also a naval action novel, but it's firmly focused on British trawler crews, the only warships beyond the Icelandic Coast Guard ships mentioned are all unnamed.