The Panerai watch made in Italy using Rolex movements is believed to be one of only 618 made between 1941 and 1943.
It was sold through Great Western Auctions on Friday for £54,560, a record price for the business.
The timepiece was found in a drawer at a house in Lanarkshire and is believed to have been taken home by a British soldier as a trophy and souvenir.
The watches were used by frogmen - “Kampfschwimmer” - of the German and Italian navy during the Second World War.
Anita Manning, managing director of Great Western Auctions, said: “The bidding was fierce.
“There was interest from Japan, Europe and America on the internet and telephone bidding, as well as from collectors in the room.
“The bidding started at £20,000 and raced upwards, with the winning bid coming from a private European collector.
“The watch was found on a routine furniture valuation in Lanarkshire.
“It had been lying unused in a drawer for nearly 70 years. The vendors, who had no idea of the value, were ecstatic with the result.”