this same bloke was an instructor to dive school in the south pacific and told me of some place called either plane or yank alley, where at the conclusion of WW2 the us systematically drove tanks, trucks, aircraft into the sea going out a mile and about 500mtrs wide, may have been an island of vanuatu, can't remember but he did have some footage of it, was sad, there was heaps of great stuff...
I suspect there are many such locations. I worked at Milne Bay briefly back in the early 70s and there was a Catholic missionary there at the time who spent all his spare time searching in the jungle for a dental hospital (with all the kit) that the Americans were said to have buried there when they moved north during the war.
There was also a site (on land) near Finchafen where some bloke had found multi layers of Kittyhawk wings when he dug a hole for some other purpose.
After the war, and after attempting without success to find a buyer**, the Americans built a huge ramp out off a cliff (I think, from memory, either at Okinawa or Iwo Jima), and drove a huge amount of equipment originally slated for the invasion of Japan off the ramp into the sea. I've seen the fim of truck after truck after truck, all apparently laden with as much stuff as could be crammed into their backs, being driven down the ramp into the sea. I'm sure it's available somewhere on YouTube. I think they did the same at quite a few places throughout the Pacific.
** The best price they could get was 5 cents in the dollar from the French, who wanted it for their campaign against the Viet Minh. They US considered that wasn't enough, so they dumped it all.
Usually, coral growth and degradation would leave the equipment in a very poor state of repair by now. However, not always so. I was in PNG in the early 70s when a USN Corsair was recovered from very deep water somewhere near the Solomons. The aircraft was in almost pristine condition, with the markings on its paintwork still easily read. Even the tyres were still inflated. Apparently, this was because the depth the aircraft happened to come to rest at was such that there was little oxygen to support the sea life that would have made a home on the wreck.
There's probably someone out there in PPruneland who'll remember that particular recovery. The pilot's body was still in the cockpit and I understand it was returned to the US for burial. I think the year was around 1970 or 71, but am not sure.
It's probably in water way too deep, (off the continental shelf), but after WW1, (and I suspect after WW2 as well), a huge number of aircraft were dumped in the sea off Sydney Heads. The aircraft, all war surplus, were given (or, more likely, sold) to Australia by the Brits so that for a short time, I understand that the RAAF had more aeroplanes than men!
Back in my Herc days, we used to drop old crypto machines in the same area, so I think it would be safe to say that the water there is VERY deep.