This was the Finnish second defensive position on the Karelian isthmus against the Soviet forces of General Leonid A. Govorov’s Leningrad Front in the 'Vyborg-Petrozavodsk Offensive Operation' (1942/16 June 1944).
Basically parallel with the 'Päälinja' main defence line but about 12.5 miles (20 km) to its rear, the position was built in 1942/44 during the 'Jatkosota' continuation War, and extended from a point to the south-east of Vamelsuu on the north shore of the Gulf of Finland across the isthmus in a north-easterly direction through Kuuterselkä and Kivennapa and along the Taipaleenjoki river to Taipale on the western shore of Lake Ladoga.
After breaking through the 'Päälinja' main defence line in the first stage of the 'Vyborg Offensive Operation', on 13 June the Soviet 21st Army’s offensive reached the 'VT-linja', which was still incomplete, and broke through it on 15 June at Kuuterselkä. Even so, the Finnish resistance had managed to impose a significant delay on the Soviet advance. At the same time, the Soviet 23rd Army attempted to break through at a perceived weak point in the 'VT-linja' at Siiranmäki, which was the first place at which Finnish troops were able to use Panzerfaust and Panzerschreck anti-tank weapons imported from Germany. Though the Finns managed to contain the Soviet breakthrough at Siiranmäki, this was not in itself sufficient to allow the Finns to hold the 'VT-linja' as it had already been breached at Kuuterselkä.
In the fighting at Siiranmäki against the Finnish 7th Regiment between 13 and 16 June, the Soviet LXXXXVIII Corps suffered 3,784 casualties, including 887 men killed.