Two divers from Kent have pleaded guilty to taking valuable items from shipwrecks and not declaring them.
David Knight, 52, of Castle Road, Sandgate, and Edward Huzzey, 55, of Granville Parade, Sandgate, admitted to a total of 19 offences between them.
Bronze cannon and propellers from German submarines were among items taken from wrecks off the Kent coast.
The men appeared before Southampton Magistrates' Court where sentencing was adjourned to 2 July.
The Maritime and Coastguard Agency (MCA) said the offences were contrary to section 236 and section 237 of the Merchant Shipping Act 1995.
The shipwrecks targeted included German submarines from World War One and an unknown 200-year-old wreck carrying English East India Company cargo.
The first known objects were removed in 2001.
The items taken included eight bronze cannon, three propellers from German submarines, lead and tin ingots and various other artefacts.
It is thought the combined value of the items is more than £250,000.
Mark Dunkley, English Heritage's maritime designation adviser, appealed to the public for their help in finding six of the cannon.
They were constructed in 1807 by W&G and have the English East India Company logo (VEIC) on them.
The MCA said it was aware from diary entries that Knight and Huzzey used explosives and sophisticated cutting equipment to free wreck material.
The items should have been declared to the MCA's Receiver of Wreck within 28 days of taking them.