The Army of the Isthmus (Finnish: Kannaksen Armeija) was a formation of the Finnish Army during the Winter War. It was stationed on the Karelian Isthmus and was the largest formation of the Finnish Army, as it was charged to defend the important isthmus.
The army was organized into two corps. At the beginning of the war it had one division in reserve. Along the Soviet border four delaying groups of smaller units was deployed.
Immediately by the border on the isthmus were the four delaying groups named after their location:
On February 25 the II Corps was split and a new I Corps was established. It was given the 1st and 2nd Divisions (former 11th Division).