Pockets of resistance

A salient, also known as a bulge, is a battlefield feature that projects into enemy territory. The salient is surrounded by the enemy on multiple sides, making the troops occupying the salient vulnerable. The opponent's front line that borders a salient is referred to as a re-entrant – that is, an angle pointing inwards. A deep salient is vulnerable to being "pinched out" through the base, and this will result in a pocket in which the forces in the salient become isolated. On the other hand, a breakout of the forces within the salient through its tip can threaten the rear areas of the opposing forces outside it, leaving them open to an attack from behind.

Salients can be formed in a number of ways. An attacker can produce a salient in the defender's line by either intentionally making a pincer movement around the flanks of a strongpoint, which becomes the tip of the salient, or by making a broad, frontal attack which is held up in the centre but advances on the flanks. An attacker would usually produce a salient in his own line by making a broad, frontal attack that is successful only in the centre, which becomes the tip of the salient.

In trench warfare, salients are distinctly defined by the opposing lines of trenches, and they were commonly formed by the failure of a broad frontal attack. The static nature of the trenches meant that forming a pocket was difficult, but the vulnerable nature of salients meant that they were often the focus of attrition battles.

In mobile warfare, such as the German Blitzkrieg, salients were more likely to be made into pockets which became the focus of annihilation battles.

A pocket carries connotations that the encircled forces have not allowed themselves to be encircled intentionally, as they may when defending a fortified position, which is usually called a siege. This is a similar distinction to that made between a skirmish and pitched battle.

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Wikipedia