Holding attack
Definition: Many standard military activities can be considered deceptive, but not deception. For example, a unit may move into an assembly area to complete organizing and rehearsing prior to a mission. It is a standard deceptive tactic to camouflage the vehicles, equipment and personnel in the assembly area with the intent of confusing the enemy. Military deception is more complex than simple deceptive activities, with a unit deliberately planning and carrying out an elaborate effort that will cause a targeted adversary decision maker to take an action that is detrimental to the adversary and beneficial to the side employing deception.

Types: Deception can be accomplished through either increasing or decreasing an adversary's understanding of the operating environment. Ambiguity increasing deception is intended to sow confusion in the mind of the enemy decision maker by presenting multiple possible friendly courses of action. Because the adversary does not know which is true, his reactions are delayed or paralyzed, which gives the friendly side an advantage. With ambiguity decreasing deception, the friendly side intends to make the adversary certain of the friendly course of action — certain, but wrong. As a result, the adversary will misallocate time, personnel, or resources, which enables the friendly side to obtain an advantage. 
The Operation Bodyguard deception in World War II can be viewed as an ambiguity increasing deception that over time became ambiguity decreasing. Initially, the aim was to increase confusion among German planners and leaders by presenting the possibilities of Allied invasions at the Pas-de-Calais and Normandy in France, as well as the Balkans, southern France, and Norway. Eventually, the deception increased certainty on the German side by causing them to conclude that Calais was the real invasion site. When the Allies attacked at Normandy, they did so with the advantage of surprise.

Tactics: Military deception may take place at the tactical, operational, and strategic levels of warfare. The five basic tactics include:

Diversion
Use of feints, demonstrations, displays, or ruses to draw the enemy's attention away from a friendly main effort and induce the enemy to concentrate resources at a time and place that is to the enemy's disadvantage.
Example: On the night of 17–18 August 1943, the Royal Air Force carried out Operation Hydra, the bombing of a World War II rocket research center at Peenemünde, a German town on the Baltic Sea. Over a period of time, the British had conditioned the Germans to expect and respond to attacks on Berlin by sending de Havilland Mosquito bombers along the same route towards the city. When the British executed Operation Hydra, the Germans believed eight Mosquitoes flying towards Berlin were the vanguard of yet another attack on the same target. As a result of this diversion, the Germans deployed the majority of their fighter aircraft over Berlin, which gave the British an advantage over Peenemünde.
Feint
An offensive action involving force-on-force contact with the adversary which deceives the adversary as to the location and/or time of the friendly side's main effort. A feint will cause the enemy to concentrate resources at an incorrect time and location. A series of feints will condition the enemy to friendly activities in the same location, causing the enemy to lower their guard or respond ineffectively to the friendly main effort.
Example: In May 1940, Nazi Germany's Army Group B attacked the Netherlands and Belgium. At the same time, Army Group A invaded France by attacking through the Ardennes towards the city of Sedan. Army Group B's attack was a feint intended to disguise Germany's main effort from British and French military leaders.
Demonstration

A demonstration presents a show of force similar to a feint, but avoids actual force-on-force contact with the adversary. The intent of a demonstration is for the adversary to incorrectly determine the time and location of the friendly main effort, which gives the friendly side an advantage by causing the adversary to incorrectly allocate resources, move to the wrong location, or fail to move.
Example: During the Peninsula campaign of the American Civil War, Union commander George B. McClellan believed he faced a stronger Confederate force commanded by John B. Magruder than he actually did. Magruder reinforced McClellan's perception with numerous demonstrations, including parading his soldiers where they could be viewed by Union observers, concealing them as they moved back to the start point, then parading them again within sight of McClellan's observers. McClellan concluded that he was outnumbered and decided to retreat.
Ruse
The deliberate exposure to the enemy of false information that causes the enemy to reach an incorrect conclusion about friendly intentions and capabilities. A ruse is a trick of warfare that relies on guile to contribute to a larger deception plan.
Example: The creation of the fictional Major William Martin ("The Man Who Never Was") as a British officer carrying important World War II battle plans. As part of the Operation Mincemeat deception that concealed the location of the planned Allied invasion of Sicily, the Allies intended for the Nazis to acquire the false documents, which indicated a planned Allied invasion of Greece and the Balkans, and then incorrectly allocate troops and materiel.
Display
The static portrayal of activity, troops, or equipment. A display is intended to deceive the adversary's visual observation capability, causing him to believe the friendly force is in a location other than where it is, that it has a capacity or capability it does not possess, or that it does not have a capacity or capability that it does possess.
Example: The Allied use of "sunshields" in Operation Bertram and inflatable decoys in Operation Bodyguard during World War II to deceive the enemy as to the size, location and objectives of Allied forces.
These basic deception tactics are often used in combination with each other as part of a larger deception plan.

Legality: Adherents to Protocol I (1977) of the Geneva Conventions agree not to engage in acts of perfidy during the conduct of warfare. Perfidious conduct is a deceitful action in which one side promises to act in good faith with the intention of breaking that promise to gain an advantage. Examples include one side raising a flag of truce to entice an enemy to come into the open and take them as prisoners of war, then opening fire on the uncovered adversary. Additional examples include misusing protected signs and symbols, such as the red cross, crescent, and crystal, to conceal weapons and ammunition by making them appear to be a medical facility.

Axioms, maxims, and principles: The development of modern military deception doctrine has led to the codification of several rules and maxims. In U.S. doctrine, three of the most important are expressed as Magruder's Principle, the Jones' Dilemma, and Care in the Placement of Deceptive Material (Avoid Windfalls).

Magruder's Principle: Named for Confederate general John B. Magruder, the principle asserts that it is easier to convince a target into holding on to a pre-existing belief than it is to convince a target of something it does not believe. Examples include the Allies of World War II making use in the Operation Mincemeat deception of the pre-existing German belief that Greece and the Balkans would be their next invasion target after North Africa, when the Allies actually intended to invade Sicily.

Jones' Dilemma: Named for British scientist Reginald Victor Jones, who played an important role in the Allied effort during World War II, the Jones dilemma indicates that the greater the number of intelligence and information gathering and transmitting resources available to the deception target, the more difficult it is to deceive the target. Conversely, the more of the target's intelligence and information systems that are manipulated in a deception plan or denied to the target, the more likely the target is to believe the deception. One reason the World War II Operation Bodyguard deception was accepted as true on the German side is that Germany's ability to acquire information about activities in England was limited, enabling the Allies to manipulate the few German intelligence gathering resources that were available.

Avoid Windfalls: If a deception target obtains deceptive information too easily ("too good to be true"), the target is unlikely to act on it and the deception will fail. This requires deception planners to take care in placing deceptive information so that it will appear to have been acquired in a seemingly natural manner. The deception target is then able to assemble details from multiple sources into a coherent, believable, but untrue story. The best deception plans co-opt the enemy's skepticism through requiring enemy participation, either by expending time and resources in obtaining the deceptive information, or by devoting significant effort to interpreting it. In an example of valid information being dismissed as a windfall, early in World War II a plane carrying German officers to Cologne became lost in bad weather and landed in Belgium. Before being arrested by Belgian authorities, the Germans attempted to burn the papers they were carrying, which included copies of the actual invasion plans for Belgium and the Netherlands. Belgian authorities discounted this true information as false because of the ease with which they obtained it.

Multiple Forms of Surprise: Friendly events about which an adversary can be deceived are described in the mnemonic SALUTE-IS, which stands for Size, Activity, Location, Unit, Time, Equipment, Intent, and Style. The maxim indicates that the more of these categories the friendly side can deceive the adversary about, the more likely the adversary is to believe the deception. Conversely, if there are plans and activities about which the adversary is already aware, attempting to deceive him about them is unlikely to succeed. In Operation Bodyguard, the Germans knew there would be an invasion on the coast of France, that it would happen in 1944, and that it would be based in England. They did not know the exact date and the exact location.