The '1st Battle of Vyborg Bay', known to the Finns as the '1st Battle of Viipuri Bay' was fought between Soviet and Finnish forces for the city of Vyborg (Viipuri in Finnish) as the culmination of the USSR’s second offensive in the 'Winter War', and was this conflict’s final battle (2/13 March 1940).
The primary Finnish defences on the Karelian isthmus were those of the 'Mannerheim-linja', and had been penetrated by the Soviet forces of Kormandarm 2-ranga Kirill A. Meretskov’s 7th Army in the '2nd Battle of Summa', and on 15 February Sotamarsalkka C. G. E. Mannerheim, commander-in-chief of the Finnish forces, had ordered a general retreat to the so-called Intermediate Line. However, the effective Soviet deployment also broke through the Intermediate Line and the Finnish troops were compelled on 27 February to fall back to the line connecting Viipuri, Tali, Noskuanselkä, Kuparsaari and the Vuoksi river.
Meretskov’s 7th Army was now ordered to launch an offensive with one direct frontal assault and two flanking movements. The X Corps and XXVIII Corps were to advance into the area to the west of Vyborg across the frozen Vyborg Bay, and the XIX Corps was to advance east of the city. The XXXIV Corps and L Corps were to attack directly toward Vyborg.
Despite many problems, these Soviet forces of the North-West Front advanced to Vyborg, and on the morning of 10 March, the XXVIII Corps secured a bridgehead, more than 3.1 miles (5 km) wide, at Vilajoki. At the same time, units of Komkor Yakov T. Cherevichenko’s III Cavalry Corps began to advance over the ice of the Gulf of Finland and concentrated on the island of Piisaari, from where it would be possible to bypass Vyborg.
However, the presence of flooded areas, logistical difficulties and constant Finnish counterattacks by Kenraaliluutnantti Karl Lenart Oesch’s Rannikkoryhmä (coastal group), Kenraaliluutnantti Harald Öhquist’s II Armeijakunta (corps) and Kenraalimajuri Taavetti Laatikainen’s I Armeijakunta prevented the Soviet forces from achieving any more visible progress, and until 12 March the fighting was so intense that both sides reached a state of complete exhaustion.
On 13 March, the Finnish delegation finally accepted Molotov’s peace conditions in Moscow, and a ceasefire came into effect at 12.00.