Two men have been arrested over the suspected theft of artefacts from sites in the Thames Estuary, including the protected wreck of HMS London, a 17th century warship.
The arrests yesterday followed raids in East Kent on two homes, one business address and a dive boat at Gravesend.
The raids were carried out by police officers from Kent and Essex, archaeologists from English Heritage and officials from the Maritime and Coastguard Agency, including the Receiver of Wreck.
At one address they found what is believed to be a 16th century Dutch cannon from the London, worth an estimated £40,000.
In clean condition it sat partially immersed in a tarpaulin-covered trough of water in a back garden.
Other artefacts found at the same address included deck fittings, lead, china, glass and portholes.
The arrested men are being interviewed at a Kent police station. Police are examining materials including business records and computer images.
The arrests follow the February launch of the Alliance to Reduce Crimes Against Heritage (ARCH), intended to harden up enforcement of heritage law.
Under ARCH, various authorities are working in a more symbiotic way to improve investigative efficiency.
Speaking at one of the raid locations Alison Kentuck, Receiver of Wreck, told the BBC that the aim was to use “the same information to the best of its ability, to share resources to achieve an end result”.