Somali pirates who attacked an American freighter with rocket-propelled grenades were not trying to capture it but to destroy it as an act of revenge, one of their commanders claimed today.

The LIberty Sun, carrying a cargo of food aid for Africa's starving millions, was attacked yesterday afternoon by two speedboats some 285 nautical miles off the Somali coast.

Its crew responded in what is becoming textbook fashion for unarmed crews in the Gulf of Aden and along Somalia's Indian Ocean coast.

They hunkered down in the engine room while the ship’s master increased speed and threw the Liberty Sun into series of twists and turns. The pirates could not get close enough to deploy their grappling hooks.

By the time the USS Bainbridge, a guided missile destroyer, arrived two hours later, the buccaneers had given up and headed off in search of easier prey. “She was able to report that the ship and crew were safe,” said Lieutenant Stephanie Murdock of the US Navy’s Fifth Fleet, stationed in Bahrain.

On board the USS Bainbridge was Richard Phillips, captain of the Maersk Alabama, who spent five days in a lifeboat with a group of pirates before the US Navy Seal snipers rescued him on Sunday, killing three pirates.

“This attack was the first against our prime target,” Abdi Garad, a pirate commander, said today. “We intended to destroy this American-flagged ship and the crew on board but unfortunately they narrowly escaped us.

“The aim of this attack was totally different. We were not after a ransom. We also assigned a team with special equipment to chase and destroy any ship flying the American flag in retaliation for the brutal killing of our friends."

Mr Garad's claim cannot be tested and could be bravado: while the pirates have the upper hand, holding 17 vessels and almost 300 seamen, unarmed crews are increasingly finding ways to avoid capture. Only about a quarter of attacks this year have been successful.

Yesterday, the crew of the Maersk Alabama flew out of the Kenyan port of Mombasa on a chartered plane home. They managed to fight off pirates who boarded their container ship last week.

They had been due to be reunited in Mombasa with their captain, Mr Phillips, who gave himself up to secure their safety, but he was aboard the Bainbridge when it was diverted to help the Liberty Sun.

“We are very happy to be going home,” said crewman William Rios of New York City. “We are disappointed to not be reuniting with the captain in Mombasa. He is a very brave man.”

The Liberty Sun was attacked en route from Texas to Mombasa. One crew member had time to describe what was happening in an email to his parents. “We are under attack by pirates, we are being hit by rockets, also bullets,” Thomas Urbik, 26, told his family in a message headed “I love you all”.

“We are barricaded in the engine room and so far no-one is hurt. (A) rocket penetrated the bulkhead but the hole is small. Small fire, too, but put out.”

The Maersk Alabama also spent five hours trying to outrun the pirates and several other ships have managed to evade capture. Crews have used high pressure fire hoses to keep pirates at bay and barbed wire is credited with protecting an Indian ship from hijacking.

It does not take much to put off a potential boarding party in search of easy pickings, according to Nick Davis, who runs the Gulf of Aden Transit Group offering advice to ship’s crews.

“If you let them know you’ve spotted them two to three miles away by blowing on your horn, increasing speed, putting your fire hoses on and adopting a gentle weave, then they’ll know you are on the radio calling in military assistance and will often give up,” he said. “Once they have lost the element of surprise then they have lost the advantage.”

However the pirates are still enjoying a bumper year, launching 79 attacks and hijacking 17 ships. Four more were taken this week, even as President Obama was promising to stem the tide of piracy.

For now, multimillion dollar ransoms ensure the pirates have a queue of volunteers ready to risk their lives at sea. Last year shipping line paid $80m in ransoms and the pirate gangs know that owners are reluctant to arm crews and would rather negotiate their rescue.

The surge in attacks is expected to last for another few weeks as the pirate season continues with flat seas and good weather. "The waves are low right now and the conditions really favourable to the pirates," said Andrew Mwangura of the East African Seafarers Assistance Programme. "We expect this to continue for at least another two weeks.”

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