The following is the April 8, 2021 Congressional Research Service In Focus report, Defense Primer: What Is Command and Control?
From the report
The Department of Defense (DOD) defines command and control (C2) as “[t]he exercise of authority and direction by a properly designated commander over assigned forces in the accomplishment of the mission.” At its most fundamental level, C2 represents how DOD makes operational decisions. One can view C2 through the context of five variables: who, what, when, where, and how (see Figure 1). Traditionally, Congress has focused on the authorities (the “who”) and technology (the “how”) variables, and less so on the force mix (“what”), temporal (“when”), and geographic (“where”). China and Russia have developed strategies to disrupt or potentially deny DOD its ability to make decisions; as a result, DOD is modernizing systems and processes to command and control military forces.
The first variable that Congress has traditionally focused on reflects the authority a commander has to execute an operation. This line of discussion focuses on the chain of command, reflecting the differences between the military services—charged with organizing, training, and equipping U.S. forces (e.g., the Army provides infantry battalions and the Air Force creates fighter squadrons)—and the combatant commands who decide what those units should do and give them orders. This variable can be summarized by the question: “who commands forces?”
The second variable represents the hardware and systems that enable commanders to make these decisions and transmit them to the field. Terms like command, control, communications (C3), C3 plus computers (C4), and intelligence, surveillance, and reconnaissance (ISR) enter the discussion. This technical dimension of command and control looks at the data (and method of collection) that commanders use to make decisions (i.e., ISR is the data to enable decisionmaking), the processing power to transform data into information (the computer element), and the systems that enable commanders to communicate their decisions to geographically distributed forces. This technical approach to command and control can be summarized as, “how do you command forces?”
Other variables of command and control answer separate questions: which systems and units are being commanded (“what”), the temporal aspect (“when”), and geography (“where”). Congress has historically expressed interest in each of these variables in the context of specific, rather than general, issues. For example, rather than considering general purpose forces, Congress has focused on issues regarding nuclear forces and authorities associated with special operations (“What forces are being commanded?”).
Regarding the “when,” Congress has expressed interest in command and control associated with quick response to nuclear and cyber operations, and to a limited extent in terms of electromagnetic spectrum operations. However, a sensitivity on “when” generally is more tactically focused (e.g., when to have aircraft on target, when an assault on a building should begin); these decisions are often delegated to operational commanders.
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