Berets of the United States Army
U.S. Army Special Forces wear the green beret because of their link to the British Commandos of World War II. The first Ranger unit, commonly known as Darby's Rangers, was formed in Northern Ireland during the summer of 1942. On completion of training at the Commando Training Depot at Achnacarry Castle in Scotland, those Rangers had the right to wear the British Commando green beret, but it was not part of the regulation uniform at the time and was disallowed by the U.S. Army. 
The 10th Special Forces Group (Airborne) had many veterans of World War II and Korea in its ranks when it was formed in 1952. Members of the 10th SFG began to unofficially wear a variety of berets while training, some favoring the red or maroon airborne beret, the black beret, or the green commando beret. In 1953, a beret whose design was based on that of the Canadian Army pattern, and which was rifle-green in color, was chosen for wear by Special Forces units.
Special Operations Troops Centre
After the creation of the special operations unit in 1981, the CTOE ceased to be just an instruction facility but also served as the HQ for the new Portuguese special operations unit. The unit members wear a grass green beret and are the heir of the Special Hunters: the beret badge includes a trumpet — a symbol of the Special Hunters; and the unit is known as Rangers because the first instructors of the Special Hunters completed the Ranger Course and adapted the characteristics of that training to the Special Operations Course. The unit has operated in Bosnia and Herzegovina, East-Timor, Kosovo, Afghanistan, and Iraq.The CTOE has several courses:For those already badged as special operations soldiers, there are also courses outside the CTOE:Special Operations soldiers also take courses in friendly countries: