Bondone said he was able to identify the P311 by the two chariots strapped to the hull.
"I found the submarine in excellent condition, only the bow is damaged from the explosion," Bondone told Discovery News.
He believes the submarine remained airtight as it sank, meaning the crew died of oxygen deprivation.
"I immediately thought of the fate of those men who died down there," Bondone said.
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HMS P311 was the only boat of its class never to be given a name, sinking before the name Tutankhamun, after the Egyptian pharaoh, was assigned.
The submarine's captain was 35-year-old Commander Richard Cayley, a war hero who distinguished himself in several missions in the Mediterranean. It was said he destroyed nearly 70,000 tons of shipping, a feat which earned him the nickname "Dead-Eye Dick."
It is highly unlikely the submarine will be moved, and the remains of Cayley and the other 70 crew members recovered.
"The P311 is now a war grave," Bondone said.
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