Submariners on board nuclear submarine HMS Victorious thought it was a wind-up when they heard that Bruce Dickinson, best known for being the lead singer of Iron Maiden, was on board with them.
The 53-year-old singer of the band, which exploded on the scene in the early eighties with their fiery brand of music, spent three nights on the submarine.
The captain of the boat is believed to have given Bruce, who is also a qualified pilot, a special invitation, to come on board and have a taster of what life is like living and working on a nuclear submarine.
One of the submariners said being in the presence of an international rock star made the routine sea exercise more interesting.
He told the Advertiser: "It was a bit surreal - it's not every day you bump into an international rock star on a nuclear submarine.
"When I heard that somebody called Bruce Dickinson was coming on board, I thought it was maybe a civilian contractor or someone who went by that nickname.
"When I saw him, I thought that he looked quite a lot like him as well and I thought it was a wind up when somebody said it was actually him."
He said Bruce was very knowledgable about the submarine and had obviously done his homework.
He added: "He was extremely down to earth and hung around with everybody asking questions and chatting about his life.
"Everyone was happy to have him on board with us. Lots of people were stunned by it but some didn't know who he was."
VIPs are sometimes invited on to the boats for a short period of time and a spokesman for Faslane confirmed that the private visit had taken place.
Iron Maiden was firmly established as heavy metal's brightest hopes when they stormed the world with their third album - and first with vocalist Bruce Dickinson - The Number Of The Beast in 1982.
The band has clocked 80 million album sales, nearly 2,000 live performances and 15 studio albums and on their website say they are the "undisputed heavy metal champions of the world".