Searching for artefacts under the sea is some of the most difficult work that archaeologists encounter. The sea, like space, is an alien environment to the human frame. Complex survival equipment must often be donned before archaeologists can make even the first scrape in the seabed.

The alternative to diving suits and air tanks is the submersible, but their use is expensive. Bob Ballard used one to find the Titanic in 1985, although he admitted last month that the expedition was a cover story for a mission to find and inspect two sunken nuclear submarines.

One of the most important things that an archaeologist will need in searching the seabed is solid research. Academics and treasure hunters can spend years studying old documents for clues of where best to begin.

Once the most likely locations have been identified the business of peering beneath the waves can start. Sonar is a tried and tested technology and among its biggest successes was the discovery of the wreck of the Mary Rose in the late Sixties. The ship was part of Henry VIII’s fleet and sank in the Solent during an engagement with the French in 1545. Archaeologists devoted years to inspecting the wreck, raising a host of artefacts and eventually lifting part of the timber hull to the surface.

Even more problematic than recovering artefacts is preserving them, and archaeologists often need to keep their finds in controlled conditions to prevent disintegration.

In clearer waters divers can search for wrecks just by scouring the seabed. Among such discoveries was that of the Quedagh Merchant, Captain William Kidd’s ship, in waters only 10ft (3m) deep off Catalina Island in the Dominican Republic.

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