Next Sunday marks a significant date for German U-boat that was raised from the deep to become a top Wirral tourist attraction.

Mystery surrounds the final voyage of the U-534 which sailed on in defiance of the May 1945 order by Admiral Donitz for all U-boats to surrender.

The submarine, which was commissioned on December 23, 70 years ago, was tracking towards Norway when she was sunk by depth charges dropped by an RAF Liberator bomber on May 5 1945.

Rumours persisted that she was carrying Nazi gold or high ranking German brass to South America. When the U-boat was raised after 41 years hopes of a treasure trove proved to be unfounded. No gold or secret passengers were found. But the mystery of why she did not surrender remained.

The vessel - rebuilt in four sections with glass viewing partitions – is now the star attraction of Merseytravel’s U-boat Story at Woodside Ferry Terminal.

The Woodside display also includes a rare German Enigma coding machine whose secrets were cracked by the British to give the allies insight into enemy intelligence.

U-534 is one of only four remaining U-boats in the world and the only one of its kind in the UK. She was transported to Wirral in 1996 after being raised from the Kattegat – between Denmark and Sweden – in 1993.

She had been found in 1986 by Danish wreck hunter Aage Jenson and seven years later media millionaire Karsten Ree sponsored the raising of the craft.

U-534 formed part of the Warship Preservation Trust’s maritime collection at Birkenhead Docks until the museum closed in 2006.

In 2007 Merseytravel acquired the submarine and the U-Boat Story opened in 2009

U-534’s early life is unclear. There is little or no record of the boat appearing in combat and it is believed that for a year and a half it was used to train new crews. The submarine only began combat duties in May 1944. It was mainly used for weather reporting and avoided contact with the enemy.