Interior lines

Interior lines is a strategy of warfare that is based on the concept that lines of movement, communication, and supply within an enclosed area are shorter than those on the outside. As the area held by a defensive force shrinks, the advantages increase.

Using the strategy of interior lines, a surrounded force can more easily supply, communicate, and move its forces around, and it can mount a series of quick attacks on the forces encircling it.

Tactic

Abstract Depiction of the advantages of interior lines in the scenario of battle field tactics.

In the context of battlefield tactics, it allows more rapid concentration of resources (firepower and manpower) and so affords greater tactical flexibility. The resources are ideally employed against an adversary at a point where they are not able to quickly respond, because of their longer external lines:

1. At the Battle of Dyrrhachium, the Optimates, led by Gnaeus Pompeius Magnus, defeated the Populares led by Gaius Julius Caesar when Caesar attempted to encircle the numerically superior Optimates at Dyrrhachium in 48 BC.
2. During the Battles of Lexington and Concord, Brigadier General Hugh Percy utilized interior lines during the British retreat, as his men were often surrounded by militia.
3. At the Battle of Jena-Auerstedt, Louis Nicolas Davout employed interior lines to defeat the main Prussian army.
4. At the Battle of Wagram, the French under Napoleon I defeated the Austrians by acquiring interior lines and achieving local numerical superiority.
5. George Gordon Meade used it against Robert E. Lee at the decisive Battle of Gettysburg in 1863.
6. Battle of Rorke's Drift. A vastly-outnumbered British force managed to defeat a Zulu army by using the advantages of the small area to defend.

By September 1950, US and South Korean Forces had been forced back to form the Pusan Perimeter in the South-East of the peninsula, giving the defenders shorter interior lines. This created a concentration of forces in defense, allowing quicker reinforcements and logistics. Fresh troops and supplies were increasingly being brought into the port in Pusan, strengthening the defense even further and preventing a North Korean victory. By contrast, the North Korean supply line had lengthened, making offensive action harder to maintain. See also Battle of Pusan Perimeter logistics.

Strategy

As a strategy, it is commonly employed to cut armies off from reinforcements supplies, or prevent allies from uniting their forces. That usually allows for an adversary that may not be numerically superior to gain a numerical superiority over an adversary in a given locality, which increases the chances of overpowering an enemy and defeating it. By extension, in overpowering an enemy, an adversary hopes to demoralize it to a sufficient degree to bring it to political terms.

Examples

After the Battle of Mondovi, the French gained the advantage of having the interior position over their adversaries in the First Coalition.

1. At the Battle of Montenotte, the First French Republic under Napoleon defeated the Austrians and destroyed an entire corps, thereby destroying the link between the Austrians and their allies Kingdom of Sardinia. As a result of the victory, the Sardinians were separated from Austria and were unable to defeat the French or rejoin the Austrians. They eventually sued for peace.
2. Frederick the Great's operational strategy, in his prosecution of the Seven Years' War against the separate armies of the French, the Russians and the Austrians, can be considered an example of the advantage of interior lines in warfare.
3. It also gave the Reds a distinct advantage over the Whites in the Russian Civil War.
4. General Robert E. Lee used the strategy during the Battle of Antietam during the American Civil War in 1862.
5. Though the Pusan Perimeter (Korea, 1950) was not an intentional strategy, the concentration of UN forces within the Perimeter allowed quick movement of supplies and reinforcements via internal lines.

See also

• Military strategy
• Two-front war