During World War II Winston Churchill decreed that his forces will set Europe ablaze, in butcher and bolt type actions by deep behind the lines Commando and Parachutist units. In the summer of 1940 he created his Special Operations Executive (SOE), referred to as "The Ministry of Ungentlemanly Warfare", which landed small or lone groups of spies, saboteurs, assassins, and liaison officers to help back and build local Resistance forces, all over occupied Europe and Africa. The USA followed suit later on with the Office of Strategic Services (OSS), and mixed Jedburgh teams. These units were relatively small, unless supporting larger bands of local resistance / partisan fighters. During the fighting in North Africa the British raised such groups as the Long Range Desert Group (LRDG) patrols, and Special Air Service (SAS) which would thrust deep behind Axis lines and attack airfields, communication centers, supply lines, garrisons etc... And then you had smaller to larger Commando formations which wreaked havoc from Norway, the Channel Islands, France, and all over the Mediterranean. Later on the SAS, SBS (Special Boat Service), and Commandos would infiltrate deep behind enemy lines and wreak utter havoc and devastation throughout the rest of the war. While the mainstream British Military was not overly pleased with these specialized bandit raiders, they had the full backing of Winston Churchill, and played a vital role throughout the war.
Both the British and the US had larger Airborne Divisions which they usually parachuted behind the lines at least at Regimental Combat Team level, if not a few divisions. These would open the way for more land forces to rush in. The Americans had a rough Commando equivalent in their Army Rangers, which would attack tough positions as a spearhead type unit. The US and Canada did have a joint Special Service Force fighting in Italy, but it too arguably operated similarly to the Rangers. In the Pacific and Asia the US did have Merrill's Marauders (an American version of the British / Commonwealth's Chindits) operating well behind Japanese lines in Burma, and Marine Raiders commando type units, and one or two Army Ranger and Paratrooper well behind the lines raids. HOWEVER, why did the USA not have an American equivalent of the SAS / SBS operating on "scoot and shoot" type attacks well behind German / Fascist lines in Europe? Were there Political reasons? Military brass pushback? Or simply, just no need for those type of Special Forces specializing in irregular warfare in a smaller / modest scale?
John A. Nagl's fantastic Learning to Eat Soup with a Knife uses the counterinsurgency examples of the British in the Malayan Emergency and the United States in the Vietnam War to compare the two military organizations' ability to culturally "learn" and react to situations on the ground. While the focus of his study is on their performance in their respective Southeast Asian encounters, Nagl goes into detail on the history of each military, and the organizational aspirations of its leadership. By its entry into World War II, Britain's military had centuries of experience retaining a vast global empire, and relying upon its troops to act as colonial police in situations where they were considerably outnumbered by existing populations and power structures. Local commanders and units were given far greater leeway in coming up with their own solutions than the formal system in Britain would otherwise have allowed, and through promotions and seniority, a significant amount of the British armed forces had institutionally adopted this idea of unit independence and strategic flexibility when faced with an uncertain enemy.
Nagl's history of the American military is very different. While John Morgan Gates's Schoolbooks and Krags details an extremely flexible American military during the occupation of the Philippines between 1898 and 1902, Nagl points to a complete lack of change to US military doctrine as a result. Instead, he details an organization developed in isolation, kept busy with frontier wars, but always modeling itself for a classical European-style battle. It constantly saw actions against Amerindian nations and other American ex-colonies as, more or less, beneath its expertise, and operated on the belief that the economic, demographic, and geographic strengths of the United States would allow it to steamroll over any foe that would dare to challenge it from across the Atlantic. This approach to warfare requires strict coordination and unbreakable discipline, which stood in sharp contrast with Britain's lack of a written military doctrine at the time. Thus, while former Secretary of State for the Colonies Winston Churchill would feel perfectly at home supporting ad hoc teams of British specialists to subdue Axis authority deep within its territory, American military leadership would only tolerate such innovations as a necessity.