Technothriller involving a Soviet covert minelayer (1979 - 1992)

[Norm017]

I am looking for a specific novel, the plot involves the Soviets using a ship, either a converted merchant vessel or one built to resemble a merchant vessel for covert minelaying. The discovery of the secret takes place in harbor.

What I am not looking for is Anthony Trew's 'The Antonov Project' or Greg Dinallo's 'Rockets' Red Glare' as I have copies of both of these books.