It is believed to be the only surviving example of the Messerschmitt 323 "Giant", a massive aircraft that was designed to carry tanks, half-tracks and artillery into battle.
The Germans initially intended to use the plane in the planned invasion of Britain, Operation Sea Lion, but it was cancelled and the aircraft instead saw action in other theatres such as North Africa and the Mediterranean.
The Me-323 was on its way from a German base in Sardinia to the city of Pistoia in Tuscany when it was shot down by a Bristol Beaufighter long-range fighter plane on July 26, 1943.
It crashed into the sea off the Maddalena islands, an idyllic archipelago of low islands and sandy beaches that is popular with sailors and holidaymakers.
A small team led by Cristina Freghieri, a diver and amateur historian, claims to have discovered the wreck at a depth of 200ft.
They spent a year trawling military archives, flight path records and local eyewitness accounts in their hunt for the unusual relic.
"It was just by chance that we found it because we were actually looking for a different plane wreck," Aldo Ferrucci, a diving instructor and photographer who took pictures of the wreck, told The Daily Telegraph.
"We had understood that the Me-323 was in a totally different location so we were lucky to stumble on it. It is in good condition – it is almost intact, with the six engines still all in line.”
The wreck, located eight nautical miles off the coast, was identified with a wire-guided camera and then explored by divers.
"It was a pure emotional charge to suddenly see the aircraft in the veiled blue of the sea. First we saw a piece of sheet metal, then another until the plane appeared in all its beauty.
My heart skipped a beat," Ms Freghieri told Ansa, an Italian news agency.
The Me-323, known in German as the "Gigant", weighed 45 tons, had six engines and boasted a wingspan of 180ft.