A catalogue of errors, from poor intelligence to inadequate training and lack of firepower, was blamed yesterday for the capture of the 15 British Marines and sailors by Iranian forces two weeks ago.

As the Ministry of Defence began an inquiry into the circumstances of the incident on March 23, when a lightly armed Royal Navy boarding party was ambushed and taken hostage by Iranian Revolutionary Guards, naval sources said that clear failings had already been identified.

It is understood that a thorough review of the rules of engagement and standard operating procedures is already under way to prevent another ambush, the second of British naval forces by Iranian vessels in three years.

One clear failure was the inadequate protection provided for the boarding party, which was equipped with only side-arms and travelling in two rigid inflatable boats (RIBs). The inflatables were no match for the six larger and better armed Iranian Revolutionary Guard Corps Navy vessels that surrounded them.

The inquiry will want to know why the Lynx helicopter flying from HMS Cornwall, which was equipped with a heavy machinegun, had already returned to the ship before the mission was complete. It was scrambled when the ambush was under way but arrived back on the scene too late to save the Marines and sailors.

“I understand that HMS Cornwall had requested a sniper team be added to its crew but this was turned down by the Ministry of Defence,” one naval source said. “That has now been rectified.”

There are also concerns that Royal Navy commanders had inadequate intelligence that may have made them complacent. Iranian military commanders had been giving warning publicly for weeks that they intended to capture American or British forces in Iraq in retaliation for the arrest in January of five Iranian officials by US troops.

British servicemen were particularly at risk on March 23 since Britain was pushing through a UN Security Council resolution the next day, imposing sanctions on Iran over its nuclear programme.

British soldiers operating in southern Iraq were put on alert earlier this year against the hostage threat. They were authorised to use “maximum force” to avoid being captured while on patrol. The same rules of engagement clearly did not apply to naval personnel patrolling Iraqi waters.

The incident has also raised doubts about whether Britain has the right ships to conduct the operations required in the shallow waters of the northern Gulf. HMS Cornwall is a Type 22 frigate that was designed to combat Soviet submarines during the Cold War.

She is too large to operate in the confined waters of the northern Gulf coast. As a result she was several miles from the boarding party when they were ambushed and so was powerless to help.

Jason Alderwick, a naval expert at the International Institute for Strategic Studies, said that the Navy needed a warship more appropriate for the job, such as a small, fast and heavily armed corvette with a shallow draft that could operate right up to the Gulf coast-line. The US Navy is already developing such a vessel, known as a Littoral Combat Ship.

The MoD will also have to review its interrogation training for personnel on active service. At the moment, only forces on the front line are trained to cope with capture and interrogation.

There was also some criticism of the behaviour of the captured sailors and Marines, who allowed themselves to be used for Iranian propaganda purposes.

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