The United States started the war with no experience in this area. Not that America was unfamiliar with secret agents and messy missions in foreign nations, but it was always done in an impromptu fashion. World War II required a more organized approach. The OSS (Office of Strategic Services) wasn't actually all that organized, but it did provide one-stop shopping when the U.S. government needed something unusual done in a dangerous place. But more important, OSS able to keep tabs on all the intelligence activity the army, navy, State Department and FBI (and a few other agencies) were involved in. The lack of coordination was noted by president Roosevelt after World War II broke out in 1939. After asking nicely, a few times, that everyone get their act coordinated and provide him with a unified picture, and being ignored, Roosevelt appointed Wall Street heavyweight William ("Wild Bill") Donovan as Coordinator of Information (COI) in July 1941 and told him to get the job done.
Donovan had won a Medal of Honor during World War I as an infantry battalion commander. He was a well connected, and well traveled, lawyer with a reputation for making things happen. But underlying Donovans reputation for action was a belief in through and well documented research. Even before Pearl Harbor, Donovan's COI researchers were providing Roosevelt with excellent reports on what was going on in Europe. Once the United States was in the war, Roosevelt and Donovan saw a need for an agency that could concentrate on secret missions. So in June, 1942, COI became OSS (the Office of Strategic Services.) Donovan had, since COI was created, recruited heavily on Wall Street and the top universities and corporations. Everyone knew there was a war coming, and working for a war hero like Donovan on "special projects" was so appealing that few declined the offer. Despite State Department and the military hostility towards the new kid on the block, OSS quickly made itself useful by sending out skilled (or at least eager and daring) operatives when the State Department or military needed them.
The OSS was never a large organization, peaking at some 13,000 men and women in 1944. About two-thirds of OSS personnel were already in the Army (or Army Air Forces), including many who joined OSS as civilians, but were then given Army ranks and training to help them do their OSS jobs better. About a quarter of OSS people were civilians, including women, and many men who were too old for military service. About ten percent were from the other military services (Navy, Marines and Coast Guard). Throughout the war, 7,500 OSS members served overseas, including 900 women. Actually, about 4,500 women served in the OSS, most in the United States. The OSS was a bargain, costing about $1.3 billion (in current dollars) throughout the war. Prices went up after the war, mainly because of high tech gadgets like space satellites. But during World War II, most work was done the old fashioned way, with agents sneaking into enemy held territory to collect information and work with local resistance organizations.
Because there was a war on, everything had to be done in a hurry, and in the rush, mistakes were made and people got killed. The British, who had been at this sort of thing for centuries, worked with the OSS as much as possible, but were careful not to work too closely with the less experienced, and thus more dangerous to be around, OSS personnel. Moreover, OSS jumped into projects as they showed up, ending the war with OSS people all over the world.
One part of OSS was really unique in intelligence history. This was the analysis operation; the Research and Analysis Branch (R&A). This work was done by 900 academics, lawyers and sundry experts who were able to carefully study situations, sort out all the details, and deliver a clear, well documented report. This had never been done before, at least not to the degree of thoroughness, speed and accuracy that R&A did it. Whatever criticisms OSS received for it's World War II work, none fell on R&A. When the war ended, many in Washington wanted R&A preserved. This was difficult, because R&A's roster read like a Who's Who of America's top academics. Most wanted to get back to their universities. But enough remained to keep the OSS analysis tradition going until the CIA was formed in 1947.
What got the most publicity was the Special Operations (SO) Branch. This operation did, back then, what U.S. Army Special Forces does today; work with resistance groups in enemy territory. OSS did this in Europe and in Asia. At one point, there were 2,000 OSS personnel in China alone. The most spectacular success was Detachment 101 in Burma. There were never more than 120 people in this unit, yet they built up an army of 11,000 local tribesmen, armed with guns flown in and were created a major distraction for the Japanese. Detachment not only collected enormous amounts of accurate data on Japanese operations in Burma, but also got involved in driving the Japanese out in 1945.
The OSS also created a very useful psychological warfare capability. At the time, this was called Morale Operations (MO) and was able to develop media manipulation techniques (rumors, and propaganda that didn't appear as propaganda) to stir up resistance to the enemy or weaken the morale of enemy troops. These activities were so popular that after the war, the U.S. Army created its own psychological warfare operation, that eventually evolved into the Special Forces (by incorporating OSS Special Operations, and a lot of former OSS people as well).
Oddly enough, the OSS was not supposed to be an espionage agency. But Donovan saw that there was much room for improvement in how agent networks were set up overseas, and that the army, navy and State Department had never really done a good job in this department. So he set up the Secret Intelligence (SI) branch. By the end of the war, the worldwide network of CIA case officers and local agents (spies) was producing so much excellent information that many people in Washington did not want to shut it down.
The OSS also got involved in the use of Ultra and Magic codebreaking. It was extremely important that these projects be kept secret, otherwise the Germans and Japanese would change their codes, requiring months of work to crack the new systems, plus the possibility that the enemy might create unbreakable systems. So the OSS set up a small, carefully selected group called X-2. This group was able to keep the secret while getting the sensitive Ultra and Magic decrypts of enemy messages. The mysterious, and powerful, X-2 people soon became known throughout the OSS as guys who knew a lot, and could veto any planned operation without having to explain why. But elsewhere in the OSS, counterintelligence (keeping enemy agents out) was weak. In Europe and Asia, the OSS was penetrated many times by communist sympathizers, and a few Nazi ones as well. Some of this was unavoidable, as the OSS often had to work with enemy soldiers and civilians to get their job done. For example, in the last months of the war in Europe, the OSS parachuted 200 Germans into Germany to act as agents. Some 18 percent of them were killed or disappeared by the end of the war. But the others proved excellent sources of information from within Germany. These men were recruited from German prisoners of war and trained by the OSS. This was not uncommon, but not every one who was recruited stayed recruited.
The OSS was also the originator of the secret lab developing odd, and often useful tools for agents and spies. While the British were already doing some of this stuff, as were all nations with spy networks, the OSS took it to a whole new level. Most of this was kept secret after the war, because a lot of this technology was still useful, especially if kept secret.
"Wild Bill" Donovan stepped on a lot of high ranking toes as he got the OSS organized and operating. Many of these offended worthies, including newly installed president Truman, were keen to put the OSS out of business as soon as the war ended. This they did by October, 1945. But Donovan had friends as well, and the State Department took in the Research and Analysis division while the Army provided a home for the Secret Intelligence and X-2 branches. By 1947, many Washington big shots realized their error, and OSS was restored as the CIA. In the 1950s, the U.S. Army Special Forces rebuilt a lot of the OSS Special Operations capabilities. In the 1980s, all the armed services contributed their special operations "operations" into the Special Operations Command. The OSS was now fully restored. New names, new agencies, but the same kinds of operators and jobs.
Massive intelligence agencies are a 20th century development. Many of these intelligence agencies also take care of "operational missions." This is where the James Bond aspect comes in. "Special operations" are sexy and, understandably, quickly caught the attention of authors of adventure fiction looking for story ideas. All the major nations during World War II had an organization (or organizations) that took care of the derring do and high risk missions. The Russians had the NKVD, which was the largest, most ruthless and secretive of the lot. The British had several, mainly the traditional MI-6 (foreign intelligence and operations). MI-5 (internal intelligence gathering) and SOE (Special Operations Executive, a temporary organization set up to take care of all the additional missions created by World War II.) The Germans also had several organizations, mainly to keep an eye on each other.