Thieves targeted a nationally-important submarine wreck lying in the English Channel, it was disclosed today.
Divers stole the torpedo tube hatch of the Holland 5, the only surviving example on the seabed of this class of submarine in the world.
The theft was discovered during a licensed dive by the Nautical Archaeology Society in June and confirmed during a survey dive last month.
Experts said a group of people would have been behind the theft but that the hatch carried very little monetary value.
English Heritage and Sussex Police today appealed for help to catch the perpetrators who are believed to have struck over the past two years.
Removing the hatch and accessing the site without a licence is illegal under the Protection of Wrecks Act 1973, police warned.
Initial inquiries suggest it has not been reported to the Receiver of Wreck, indicating an offence may also have been committed under the Merchant Shipping Act.
The Holland class of submarine became obsolete in the early 20th Century and in 1912 the Holland 5 was destined for scrap.
It was being towed to Sheerness in Kent when she foundered and sunk six miles off the coast near Eastbourne, East Sussex.
One theory was that it took on water after the hatch that was stolen was left open.
Described as a remarkable piece of British naval heritage, the wreck remained undiscovered until the mid-90s when she was found by chance by a diver, according to the Nautical Archaeology Society.
Ministers granted protection of the wreck in 2005 to prevent it from being damaged by unauthorised interference from divers.
Speaking of the theft, Mark Beattie-Edwards, of the Nautical Archaeology Society, said: "From a monetary perspective, the hatch has very little value.
"These things are not recovered for their monetary value. They are taken as an item for someone's personal collection somewhere.
"The weirdest and strangest things sometimes have great interest for people. We don't know how many people it would have taken to remove.
"But it would have required lifting gear to bring it to the surface and may well have been brought onto a boat. It's not just a one-person theft.
"This would have required a group of people and it's probably now part of someone's personal collection."
The Holland class of submarines were the first submarines to enter service in the British Navy following extensive trials, English Heritage said.
Many developments were made and several ideas were taken back to the United States, including the first application of a periscope to a submarine to allow surface vision whilst the boat was submerged.
English Heritage said that, as a result, the wreck of the Holland 5 was crucial to the history of the early development of submarine technology.
A spokesman said: "English Heritage reported the matter to Sussex Police on August 26 and are working closely with them to bring offenders to account and to recover this nationally important asset.
"It had been impossible to visit the site in 2009 due to bad weather and the last positive sighting of the hatch was in September 2008.
"The submarine appears to have significant marine growth in the area the hatch was removed which might indicate the hatch was removed some time ago."
Sussex Police appealed for anyone with information to call them on 0845 6070 999, or Crimestoppers on 0800 555 111.Reuse content