Careful selection, integration, and analysis distinguish intelligence from other information. In the United Sates, where practitioners have made a greater effort than in most other nations to develop a conscious theory of intelligence, the terms "intelligence cycle" and "intelligence process" now denote the procedure by which information is brought to the support of policymakers. Because in the theory the word "process" is also used as a verb—to mean the act of taking information and converting it into useful intelligence—this essay will use the term "intelligence cycle."
The intelligence cycle consists of a number of sequential stages, beginning with realization of what is unknown or uncertain. Officials can ask to find out about those subjects, or intelligence officers themselves may point out a gap in information, actions that lead to an order to collect data on that topic, known as an "intelligence requirement." Some kinds of information can come only from particular sources, so the capability to gather data from a particular source may be limited, or indeed there may be several ways to get at a piece of knowledge. This means that how to meet an intelligence requirement is a matter of choice, another stage of the cycle. The act of choosing how to gather given intelligence is known as "collection tasking." What many people think of as the totality of intelligence—the act of actually securing the data—is a stage of the cycle called "collection."
In principle, in developing any kind of fact-based knowledge, collection must necessarily be by source, while appreciation is by subject. Many facts from a variety of sources may bear on a given subject. Different sources might be a photograph, a radio intercept, a newspaper article, a report from a spy, a diplomatic exchange, a scholarly paper, a radio broadcast, or the like. A given source may supply information on more than one subject, and subjects can be as diverse as a nation's military power, its economic position, or the health of a leader. Therefore, an act of transformation must occur in the cycle; this is termed "processing." The American conception is that "raw" information data is processed to become "finished intelligence." Occasionally, raw dispatches are given to policymakers, but most often they benefit from the skills of professionals who analyze the data to compile finished intelligence reports. This analysis is a further stage of the intelligence cycle, and the act of printing or otherwise creating the finished report, called "production," is another. Of course, the report is useless unless it actually reaches the policymaker who needs it; circulation of finished intelligence constitutes a stage of the cycle called "dissemination." Users of the data can then supply feedback on what they liked or did not like, or what they still want to know or find out, thereby completing the cycle by generating new intelligence requirements. Obviously, this is an oversimplified account of a series of repeated and interrelated steps that may impact on each other as well as on the finished intelligence report, but it does supply a basic picture of how intelligence is derived.
To make this picture more concrete, consider the Cuban missile crisis of 1962. In that event of Cold War history, the United States was gravely concerned over Russian military aid to Cuba. President John F. Kennedy publicly warned the Soviet Union not to supply Cuba with certain types of weapons. That created a collection requirement for U.S. intelligence to verify that the specified categories of weapons were not in Cuba. Russian cargoes arrived in Cuba by ship, and the United States had a number of spies in Cuba, as well as reports from Cuban refugees arriving in the United States. In addition, the United States had access to diplomatic and intelligence reporting from allied nations, primarily the United Kingdom and France. U.S. intelligence also had its own diplomatic and intelligence reporting from Eastern European countries and direct from the Soviet Union. These sources enabled U.S. intelligence to see that Soviet shipments were arriving in Cuba in great numbers.
The Central Intelligence Agency, one of the primary entities in the American effort, responded with a program of aircraft reconnaissance over Cuba, using U-2 spy planes to photograph suspicious targets. One U-2 flight brought back pictures that caused the CIA director to suspect the Russians of deploying weapons (antiaircraft missiles) in such fashion as to deny a reconnaissance capability over Cuba, an action he believed was intended to enable the quiet placing of Soviet offensive weapons (the kind Kennedy had warned against) in Cuba. A few weeks later, several refugee and agent reports indicated a possibility that offensive missiles were being deployed at certain locations in Cuba. Previous intelligence reports by the CIA and the U.S. intelligence community, called national intelligence estimates (NIEs), had found no offensive weapons in Cuba, but additional U-2 flights were eventually scheduled, and one of them checked the suspect areas identified by agents. That flight discovered Soviet missiles on 14 October 1962, leading President Kennedy to decide on a quarantine (blockade) of Cuba and other diplomatic actions. Maritime intelligence subsequently kept close track of the progress of Soviet ships steaming toward Cuba, aerial intelligence monitored the cargoes aboard the ships and the progress of the missile sites in Cuba, and intelligence reports thereafter kept Kennedy closely informed.