A new special forces regiment is to be operational from Wednesday, Defence Secretary Geoff Hoon has announced.
The new regiment will provide support for overseas operations
The Special Reconnaissance Regiment, or SRR, will provide specialist support for overseas operations, particularly those against international terrorism.
Recruits have been drawn from all three services, with some of the regiment's posts open to women.
The new regiment will have its headquarters in Hereford, where the SAS is already based.
"The creation of the Special Reconnaissance Regiment demonstrates our commitment to shaping our armed forces to meet the ongoing challenge of tackling international terrorism," said Mr Hoon.
"The new regiment will help to meet the growing need for special reconnaissance capability."
The Ministry of Defence (MoD) said "special reconnaissance" covered "a wide range of specialist skills and activities related to covert surveillance".
The SRR will be deployed to support both existing special forces and conventional forces in a variety of military operations.
Its creation is separate from that of the "ranger" unit, which will be formed from the 1st Battalion The Parachute Regiment and will also support special forces.
Charles Heyman, senior defence analyst for Jane's Consultancy Group, said the lack of an announcement of extra funding for the new battalion was "worrying".
Mr Heyman said: "The only worry is that we don't see any large scale extra funding, which would be nice to see.
"The worry is that we won't see the sophisticated equipment needed for a regiment of this kind."
An spokesman said the MoD could not comment on funding for the SRR because of "security reasons".
The need for a special reconnaissance unit was first identified by the Strategic Defence Review "new chapter" in 2002 and it will be a part of the UK Special Forces group.