The battle of Hattuvaara began, perhaps a bit unexpectedly, in the early morning of 30 July  1944, in the vicinity of Sikrenvaara and Kiukoinen on the road that now ends at the easternmost point of the continental European Union. After engaging the enemy successfully and repelling an assault by two battalions of the Red Army’s 52nd Rifle Regiment, the Finnish Task Force Sirama got a short respite. 

The Finnish brought reinforcements to Hattuvaara and merged these with the units already in the area. The resulting formation was designated Task Force Ehrnrooth, after Colonel Gustaf Ehrnrooth, commander of Häme Cavalry Regiment. 

Ehrnrooth received an order to push the Russian forces back the way they had come, continue the advance via Hullari across the present-day border, and then participate in the elimination of enemy pockets that would be formed in the area. The time of departure was set at 01:00 on 31 July 1944. 

Enemy forces that had fought near Kiukoinen had begun retreating toward the far bank of the Polvikoski rapids via a bridge that crossed the Koitajoki River downstream of the present structure. The road leading to the old bridge, which was much lower and narrower than the current one, remains discernible even today. 

The Finnish forces arrived near the bridge at 06:00 after a five-hour high-speed pursuit. The leading platoon dashed across the bridge but was quickly driven back by fierce machine gun fire. The crossing of the Koitajoki at Polvikoski and follow-on actions were considered of such importance that Task Force Ehrnrooth was directly subordinated to Major General Erkki Raappana less than three hours later. 

During the morning, the Finnish forces sent scouts downstream to find a place where the river could be forded, thereby enabling an attack against the rear of the enemy force that held positions behind the bridge. They began the attack by firing an artillery barrage across the river. The enemy was then dislodged and forced to retreat, chased by the Finnish forces in the direction of Hullari. Despite the Russian troops putting up delaying actions, they were pushed back over twelve kilometres in less than 24 hours, which was a commendable achievement by the Finnish troops.