After the Red Army’s 155th Division occupation of  Möhkö village on 6 and 7 December 1939, the numerically inferior Finnish forces were in an untenable situation. The combat strength of the 11th Independent Battalion that fought the delayed action had been only 800 men at the outbreak of the Winter War (1939 to 1940). Retreat to Oinassalmi was the defenders’ only remaining option. 

The Finnish forces destroyed the iron bridge at Oinassalmi on 14 December. The road leading to the bridge, which had been opened to traffic only four months earlier, ascended a rocky hillside, and the Finnish gunners could easily knock out five leading tanks at point-blank range. 

The Russian forces tried first to penetrate the defenders’ rear near Lake Mölkälampi to the northwest of Oinassalmi. It was a pivotal day for the overall situation, because at the same time fighting erupted around Lake Taivallampi five kilometres from Oinassalmi in the direction of Ilomantsi parish village. 

The Finnish troops managed to hold their positions in both locations. By the end of the year, the situation at Oinassalmi had stabilised, although a narrow stretch of water called Kääntämänsalmi, five kilometres to the southwest, remained a potential hotspot throughout the Winter War. 

The Russian forces withdrew from Oinassalmi after the end of the Winter War on 13 March  1940, as agreed in the peace talks. Work to replace the destroyed bridge with a wooden structure started early in the spring of 1940 because the road connection was essential for reconstruction work and the return of evacuees. Yet just over a year later, troops marched once again across the bridge. The Continuation War begun on 25 June  1941, and the Finnish troops were deploying toward Kuolismaa to retake those areas of Ilomantsi that had been lost to the Soviet Union in the Winter War. 

A memorial was erected at Oinassalmi in 1959 to commemorate the defenders of Tolvajärvi–Oinassalmi–Kallioniemi line. A nearby information board explains the connection between the Ilomantsi battles and major operations that took place around Tolvajärvi, to the south. A restored machine gun nest is located near the board.The present bridge was built in 1966 using the drawings of the original structure.