Excited historians likened the discovery, if verified, to finding the Titanic, as they hailed the American billionaire for his high-tech mission that apparently succeeded after so many failed search attempts by others.
Allen posted photos and video online of parts of what he said was the battleship Musashi, found by his M/Y Octopus exploration vessel one kilometre deep on the floor of the Sibuyan Sea.
"World War II battleship Musashi sank 1944 is found," Allen announced in a Twitter post that has been re-tweeted close to 19,000 times.
"I am honoured to play a part in finding this key vessel in naval history and honouring the memory of the incredible bravery of the men who served aboard her," Allen said.
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Undersea footage on Allen's website showed what were described as a valve, a catapult for planes, a gun turret and a starboard anchor.
It also showed the space on the bow for the Japanese empire's Chrysanthemum seal.
"I'm almost certain that what was discovered is the battleship Musashi," he said, adding the find had huge historical importance.
"There have been so many efforts over the years to locate Musashi, but they all failed. I feel like the warship might have been destined to show itself this year -- the 70th anniversary of the end of World War II," Todaka said.
"With the memory of war slipping further and further from people's minds, I hope this discovery will help make the public think about history.