In the context of international relations, covert action is any of a range of activities, intended to affect the behavior of a target nation or non-national actor, where the fact of the action is known, but the responsibility for the action cannot be proven. Such activities include assassination, guerrilla warfare, information operations, "gray" and "black" psychological warfare, sabotage, and subversion.
These may be conducted by units of intelligence agencies or military services, independently or in cooperation with people nominally associated with the target actor.
This complex and controversial subject, first, begins with legality. In customary international law, it is considered licit to take a specific action to kill or otherwise neutralize a key member of the enemy's uniformed military. This still may require high-level approval, for a variety of reasons, as with the deliberate interception and shooting down of the aircraft carrying Japanese Admiral Isoroku Yamamoto.
Things become much more complex when a head of state or government wears military or paramilitary uniform, but is not purely involved with military matters, as with Reinhard Heydrich, Saddam Hussein, or Muammar Khadafi.
Contrary to "common knowledge", assassination is not forbidden by U.S. law. It is, however, forbidden by a Presidential Executive Order, originally 11905, which could be revoked by any President. Subsequent Presidents have, in fact, relaxed it.
See main article on information operations; this is focused on aspects done as part of covert action.
Rather than blowing up a radar, a covert action specialist might suggest placing remotely triggerable electronic deception or jammers near it.
Computer network operations
This is more of a measure to support covert action, rather than an action in and of itself. It prevents the opponent from identifying what the covert actor intends to do, or has done.
Historically, many of the military and civilian covert action organizations of the United States came from psychological warfare, rather than existing intelligence operations. In the Second World War, the Office of Strategic Services was spawned from the Office of War Information. United States Army Special Forces were created by the Psychological Operations Division of the Army Staff.
Definitions below come from the Operations Coordinating Board (OCB), which, in 1954, was the White House organization that approved or disapproved covert and clandestine activities. Policy-level control has always been under the Department of State.
In U.S. doctrine, the term "propaganda", without further qualification, is intended to be descriptive and emotionally neutral:
Any form of communication in support of national objectives designed to
influence the opinions, emotions, attitudes, or behavior of any group in order to benefit thesponsor, either directly or indirectly.
White is acknowledged as a statement of U.S. Government policy, or emanates from a source associated closely enough with the U.S. Government to reflect an official viewpoint. The information is true and factual. It also includes all output identified as coming from U.S. official sources.
Authorized to engage in white activity directed at foreign audiences are: The State Department, USIA, the Foreign Operations Administration (a predecessor of the Agency for International Development), the Defense Department and other U.S. Government departments and agencies as necessary
The source of gray propaganda is deliberately ambiguous.
The true source (U.S. Government) is not revealed to the target audience. The activity engaged in plausibly appears to emanate from a non-official American source, or an indigenous, non-hostile source, or there may be no attribution.
Gray is that information whose content is such that the effect will be increased if the hand of the U.S. Government and in some cases any American participation are not revealed. It is simply a means for the U.S. to present viewpoints which are in the interest of U.S. foreign policy, but which will be acceptable or more acceptable to the intended target audience than will an official government statement.
Responsibility for gray is assigned to the OCB designee, USIA and State. The following criteria will assist in determining the responsibility for the execution of a proposed gray activity. If the answer to any of the three questions below is affirmative, the activity is the sole responsibility of the OCB designee. If government interest is not to be revealed but the answer to all three questions listed below is negative, the activity may fall within the charter of State, USIA or the OCB designee:
a. Would the disclosure of the source occasion serious embarrassment to the U.S. Government or to the agencies responsible for theinformation activity?
b. Would the activity or the materials disseminated be seriously discredited if it were to become known that the U.S. Government wereresponsible?
c. Would the outlet be seriously damaged if it were to become known that the activity is subsidized or otherwise assisted by theU.S. Government?
The activity engaged in appears to emanate from a source (government, party, group, organization, person) usually hostile in nature. The interest of the U.S. Government is concealed and the U.S. Government would deny responsibility. The content may be partially or completely fabricated, but that which is fabricated is made to appear credible to the target audience. Black activity is also usually designed to cause embarrassment to the ostensible source or to force the ostensible source to take action against its will.
Black propaganda can be considered clandestine, as the source is unknown.
Responsibility for engaging in black propaganda and other related activities is assigned solely to the designee of the OCB. Likewise it should be kept in mind that activities, either gray or black, conducted into denied areas from their peripheries, other than radio, are the sole responsibility of the OCB designee.
In US doctrine, black propaganda rarely is employed below the strategic level, due to the stringent coordination and security requirements needed to protect its actual source. Further, black propaganda, to be credible, may need to disclose sensitive material, with the damage caused by information disclosure considered to be outweighed by the impact of successful deception. 
- Ford, Gerald W. (18 February 1976), Executive Order 11905: United States Foreign Intelligence Activities, Executive Order 11905
- Paper Prepared by the Operations Coordinating Board: Principles to Assure Coordination of Gray Activities, vol. Foreign Relations of the United States, 1950-1955: The Intelligence Community, May 14, 1954, FRUS document 181
- Joint Chiefs of Staff (12 April 2001(As Amended Through 12 July 2007)), Joint Publication 1-02: Department of Defense Dictionary of Military and Associated Terms
- FM 3-05.30/MCRP 3-40.6 Psychological Operations, April 2005