Britain today said 200 commandos were immediately available to join the US-led coalition against Afghanistan.
Armed Forces Minister Mr Adam Ingram said another 400 commandos would be put on high readiness as Britain stepped up its contribution to US President Mr George W. Bush's war on terrorism.
Mr Ingram told the British parliament an 11-strong armada, led by the aircraft carrier HMS Illustrious, would be switched from "Exercise Swift Sword", which ends off Oman this weekend, to link up with coalition forces.
"This powerful force totals some 4,200 personnel in theatre. It represents a major enhancement of the coalition's capabilities," Mr Ingram said. "We are in this for the long haul and we mean it".
The first 200 commandos ready for the frontline would be stationed on the assault ship HMS Fearless. The other 400 will return to Britain after the Omani exercise but will be held at high readiness.
Until now, Britain's offensive contribution has been confined to three submarines launching missile attacks. Ten specialised refuelling and reconnaissance aircraft have also been supporting the Americans.
An Omani defence official said the Gulf Arab state had made it clear no attacks will be launched from its territories.
British officials said the troops would move out of Omani territory before joining other forces engaged in the raids.