The final resting places of six German U-boats sunk in the final months of the Second World War's greatest naval conflict have finally been identified. After years of research, maritime experts say their discoveries will force historians to re-evaluate the battle for control of the Atlantic.

Evidence from the wrecks suggests many U-boats were sunk by mines rather than attacks by Allied air and naval forces, as had previously been believed. The findings show coastal minefields were around three times more effective than British naval intelligence gave them credit for. Experts believe their view was distorted, unintentionally, by reports from over-enthusiastic airmen and escort ship commanders who sometimes claimed they had sunk U-boats with depth charges or anti-submarine mortars.

One submarine, the U-400, previously believed sunk by Royal Navy depth charges south of Cork in Ireland, has now been identified off the coast of north Cornwall. The German sub was on its very first patrol in December 1944 when it hit a mine, underwater photography suggests.

Another, the U-1021, also identified off the north Cornish coast, was on its first patrol in March 1945 when sunk by mines. Previously, it was thought the Royal Navy had sunk it with depth charges hundreds of miles away, off the west coast of Scotland. The U-326, also on its first patrol when it was destroyed by a US aerial depth charge attack in April 1945, has been identified 100 miles off the coast of Brittany. The U-325, sunk on its second patrol in May 1945, was thought to have been destroyed by Royal Navy depth charges in the Irish Sea. Now marine archaeology and underwater photography have identified it on the seabed 230 miles away – off Lizard Point, south Cornwall.

Other U-boats, sunk far from British coastal minefields, have also been identified. The U-1208, on its first patrol, was identified off the Scilly Isles after being sunk by Royal Navy depth charges in February 1945. The U-650, recently identified through underwater photography near Land's End, was sunk by a direct hit from a hedgehog anti-submarine missile in January 1945.

From 1939 to early 1943, the Germans were very successful in their U-boat operations – sinking 2,500 Allied merchant ships and around 50 Allied warships, with the loss of around 25,000 lives. The tide turned in May 1943 when, with new equipment and a fresh strategy, the Allies got the upper hand.

The discoveries came from a survey of the western English Channel and adjacent areas, undertaken by the US firm Odyssey Marine Exploration. Dr Axel Niestlé, a German U-boat historian involved in the project, said: "It is a fine example of successful teamwork between marine archaeologists and historians rewriting naval history. The underwater photography gave us an unparalleled opportunity to learn how different types of Second World War anti-submarine weaponry worked."

From 1939-45, the Germans built 1,167 U-boats, 863 of which were deployed in the Battle of the Atlantic; 648 were sunk – with a loss of around 25,000 submariners. The locations of 40 U-boats remain a mystery. Thirty disappeared in deep water in the Atlantic, and it is unlikely they will be found. The remainder lie in a variety of suspected locations in the eastern part of the English Channel, where the team hopes to find them.