An elite force has been set up to strengthen counter-terrorism and support special forces, Defence Secretary John Reid has confirmed.
Soldiers will bear the unit's own insignia
The Special Forces Support Group (SFSG) based in Wales, will be drawn from Royal Marines, Parachute Regiment and the RAF Regiment.
Its insignia is a dagger run through by a lightning flash.
Based at St Athan, the SFSG will train with special forces to be deployed around the world at short notice.
In a statement to the House of Commons on Thursday, Defence Secretary John Reid said: "The new Special Forces Support Group will enhance the capability of the UK Special Forces to operate around the world and will provide the UK with an additional counter-terrorist capability.
"I am pleased to be able to inform the House that the new Special Forces unit stood up, as planned, in St Athan, near Cardiff on 3 April."
The Ministry of Defence (MoD) said selection courses would involve arduous physical selection and high-quality infantry training.
The personnel will be equipped and provided with additional training to fit their specific specialist role on joining the SFSG.
The MoD said "several hundred" soldiers were involved with the unit, and some had already been deployed overseas.
Another new unit, the Special Reconnaissance Regiment, was created last year.
The tasks which will be assigned to the SFSG have previously been carried out by other units on an ad hoc basis.
One example of the type of work was from 2000 when a company of 1 Para attacked a rebel camp in Sierra Leone as Special Forces units rescued hostages from a separate camp, preventing rebel reinforcements from disrupting the rescue.
Welsh Secretary Peter Hain said of the announcement: "Confirmation that the Group is located at St Athan, close to the SAS headquarters in Hereford, is a welcome boost for the base.
"St Athan is in the process of bidding to be the site of a new proposed military academy as part of the Defence Training Rationalisation, and today's announcement is a testament to the excellent facilities that the base offers."