A commercial diver has admitted a £46,000 fraud after removing three cannon from a 17th Century shipwreck.
Vincent Woolsgrove, 48, from Minster Road, Ramsgate in Kent, pleaded guilty at Southampton Crown Court.
Essex Police found photographs proving he had taken the Dutch cannon from the London wreck. It sank off Southend in Essex in 1665. It was excavated by Historic England last summer.
Woolsgrove will be sentenced at Southampton Crown Court on 4 September.
He sold the cannon by auction to an American buyer in 2010 and they are now part of a private collection in Florida.
PC Andy Long said the case was "very rare" but his actions had deprived "future generations from viewing and understanding the county's rich history".
Police began an investigation with the UK Maritime and Coastguard Agency in 2011 and Historic England after receiving reports divers were stealing "cultural objects of historic value" from wrecks off the Essex and Kent coasts.
When they searched Woolsgrove's house, they found a 24lb (11kg) 16th Century Zierikzee cannon in a desalinisation tank in his garden, and other wreck items including ship's bells and glass ingots.
He claimed the three cannon sold in 2010 were found in international waters, but officers discovered photographs on his computer which showed them being recovered off Southend.
This evidence helped historians establish they were issued to Dutch ships in the 1650s, taken as prizes by the English and later placed on the London.
As a result, the cannon belonged to the Crown and Woolsgrove had made a fraudulent declaration about where they were found.
Essex Police said had he declared the find "he would have been in line for a substantial salvage reward".
The Maritime and Coastguard Agency is working with US authorities to arrange for them to be returned to the UK.