puolustuslinja

Puolustuslinja, in Finnish usage, is the term for a defense line or line of defense. It refers to a sequence of defensive positions and supporting measures designed to slow, channel, or stop an attacking force. A puolustuslinja typically combines natural terrain features such as ridges, rivers, and lakes with man-made fortifications, obstacles and integrated firepower, supported by logistics and command and control arrangements. The concept emphasizes delaying action, conserving forces, and concentrating combat power at decisive points, often with reserves, artillery, and air defense coordinating the defense.

Historically, Finland has used the term to describe several well-known defensive systems. The Mannerheim Line (Mannerheim-linja) on the Karelian Isthmus was developed before and during the Winter War of 1939–1940 as a major border defense. Another example is the Salpausselkä Line, a southern Finnish fortification network that formed part of the defense in the same period and during subsequent conflicts. These lines were intended to halt or slow large-scale offensives, buy time for mobilization, and create favorable conditions for counterattacks.

In contemporary doctrine, puolustuslinja remains a generic concept for layered defenses that aim to channel an adversary and protect key areas. It is used to describe both physical defensive networks and organizational approaches that link terrain, fortifications, firepower, mobility, and logistics to create a cohesive defensive posture.