Why do the Special Forces wear green berets?
Green beret
In the United Kingdom all Royal Marines who have passed the Commando Course wear the green beret.  Personnel from the Royal Navy, British Army, and Royal Air Force volunteering for service with 3 Commando Brigade  undertake the All Arms Commando Course, completion of which allows individuals to wear the headdress. Commando-qualified Royal Marines always wear the green beret, with the Globe and Laurel cap badge and commando-qualified personnel from other armed services wear the beret, with their own cap badge, when serving with commando units unless otherwise authorised.[6] The Special Boat Service (SBS) also wear the green Commando beret but with their own unique cap badge consisting of a sword with two blue waved lines with the words "by strength and guile"