Encirclement is a military term for the situation when a force or target is isolated and surrounded by enemy forces.
This situation is highly dangerous for the encircled force: at the strategic level, because it cannot receive supplies or reinforcements, and on the tactical level, because the units in the force can be subject to an attack from several sides. Lastly, since the force cannot retreat, unless it is relieved or can break out, it must either fight to the death or surrender.
Encirclement has been used throughout the centuries by military leaders, including generals such as Alexander the Great, Khalid bin Waleed, Hannibal, Sun Tzu, Yi Sun Shin, Shaka Zulu, Wallenstein, Nader Shah, Napoleon, Moltke, Heinz Guderian, von Rundstedt, von Manstein, Zhukov, and Patton.
Sun Tzu and other military thinkers suggest that an army should be not completely encircled but should be given some room for escape, or the 'encircled' army's men will lift their morale and fight till the death. It is better to have them consider the possibility of a retreat. Once the enemy retreats, they can be pursued and captured or destroyed with far less risk to the pursuing forces than a fight to the death. Examples of this might be the battles of Dunkirk, in 1940, and the Falaise Gap in 1944.
The main form of encircling, the "double pincer," is executed by attacks on the flanks of a battle whose mobile forces of the era, such as light infantry, cavalry, tanks, or Armoured Personnel Carriers attempt to force a breakthrough to utilize their speed to join behind the back of the enemy force and complete the "ring" while the main enemy force is stalled by probing attacks. The encirclement of the German Sixth Army in the Battle of Stalingrad in 1942 is a typical example.
If there is a natural obstacle, such as ocean or mountains on one side of the battlefield, only one pincer is needed ("single pincer"), because the function of the second arm is taken over by the natural obstacle. The German attack into the lowlands of France in 1940 is a typical example of this.
A third and rare type of encirclement can ensue from a breakthrough in an area of the enemy front, and exploiting that with mobile forces, diverging in two or more directions behind the enemy line. Full encirclement rarely follows, but the threat of it severely hampers the defender's options. This type of attack pattern is centerpiece to Blitzkrieg operations. Because of the extreme difficulty of this operation, it cannot be executed unless the offensive force has a vast superiority, either in technology, organization, or sheer numbers. The Barbarossa campaign of 1941 saw some examples.
The danger to the encircling force is that it is, itself, cut off from its logistical base; if the encircled force is able to stand firm, or maintain a supply route, the encircling force can be thrown into confusion (for example, Rommel's "Dash to the Wire" in 1941 and the Demyansk Pocket in 1942) or be comprehensively destroyed (as during the Burma campaign, in 1944).
A special kind of encirclement is the siege. In this case, the encircled forces are enveloped in a fortified position in which long-lasting supplies and strong defences are in place, allowing them to withstand attacks. Sieges have taken place in almost all eras of warfare.
Examples of battles of encirclement: