BOMB disposal experts helped to avert a potential disaster after an oil tanker's anchor ruptured an old torpedo in the sea off Portland.

Crew of the merchant ship, carrying 1,000 tonnes of fuel, got a shock when the anchor dragged up a test missile which had been lying at a depth of about 15-metres.

The anchor fluke had pierced the torpedo in a freak accident.

Although it was decades old and heavily corroded, Navy experts had to treat the torpedo as "live".

Test torpedoes can contain highly flammable propellant and so to be safe, the device was destroyed on the seabed in a controlled explosion once it had been safely removed.

The whole operation took seven hours.

The torpedo is believed to have come from a test range that existed for Portland until the 1980s, and had remained undetected until the anchor of the tanker Skaw Provider speared it.

Portsmouth-based Southern Diving Unit 2 was dispatched to the scene where they evacuated the majority of the crew.

However six, including the skipper, stayed on board in readiness to fight any fires that could have broken out as a result.

Officer in Charge of the diving unit Lieutenant Commander Jonathan Campbell said: "The tanker was carrying approximately 1,000 tonnes of fuel or oil.

"The fuel cargo was pumped into the aftermost possible tanks to reduce the effects of any explosion, and fire hoses were charged and ready to deploy if needed.

"We directed the ship to use her other anchor to steady her, before lowering the fouled anchor, and the torpedo, to several metres below the waterline."

The Royal Navy divers – who are Explosive Ordnance Device (EOD) specialists – had to then approach the torpedo and use their expertise to remove it in a safe manner.

Lt Cdr Campbell said: "EOD operators are obliged to treat these items as 'live' and hazardous until it can be disproved otherwise.

"The entire job was conducted in this way.

"Working parts inside the torpedo could be seen from where the anchor fluke had ruptured it. The entire bomb disposal team were professional and got on with the job in hand."

Once the torpedo was released the team then took it to a safe area, lowered it to the seabed and destroyed it.

Lt Cdr Campbell added: "The team were thoroughly relieved to be separated from their unwelcome burden."