A specially-designed British auto-submarine has surveyed the underside of Antarctic icebergs for the first time - and survived.

Built by the Southampton Oceanography Centre, the craft cost around £5 million to develop and can dive to depths of around one thousand metres. Astonishingly, it is powered by 4,700 ordinary household batteries.

Autosub being launched into the icy Southern Ocean

Autosub, as it has been dubbed, was originally sent to Antarctica on board the RRS James Clark Ross to study ice thickness and krill, which are shrimp-like animals on which seabirds and mammals feed.

It used sonar equipment to survey the underside of the iceberg, producing ultrasound images of its shape. Professor Gwyn Griffiths, Head of the Autosub team, said: "It was a very anxious time as if anything were to go wrong Autosub would be trapped under the ice."

Engineers checking their instruments

A spokesman for the Southampton Oceanography Centre said: "Usually only nuclear submarines are capable of going beneath an iceberg. The sub is battery-powered - it has around 4,700 batteries inside it - and it is completely autonomous. It is not radio-controlled but finds its own way round using sonars. That is why we are so pleased that it managed to return to the surface safely."

So far, Autosub has completed three missions diving beneath icebergs in the Antarctic. It has already been used in research on fish stock populations, mapping underwater sand-banks in the North Sea and making oceanographic measurements in the Strait of Sicily. The Autosub team returns to the UK on 20th February.