For Your Eyes Only (1986)

From the back cover:

Can you win the race to salvage the security of Great Britain?

BRIEFING: The British spy ship St. Georges has mysteriously sunk off the Albanian Coast... with the Automatic Targeting Attack Computer (ATAC) onboard! Whoever has the ATAC can order British submarines to launch their nuclear missiles — even at Great Britain itself. Sir Timothy Havelock had located the wreck of the St. Georges for M.I.6, but he was killed and his notes stolen. The enemies of Great Britain would pay handsomely for the ATAC, so every mercenary and enemy agent around the lonian Sea is after it.

MISSION: Your only lead is an assassin-for-hire who might have carried off Havelock's notes. The trail takes you to breathtaking Cortina, where lies and danger are as deadly as the speeding slopes; to the bottom of the Ionian Sea, whose usually calm depths explode with peril. Desperately you race against time and rivals while encountering deceitful beauties, deadly henchmen and cliff-hanging excitement.