February, the Russians issued a surrender demand for the fort, but this was refused by the Swedes. The demand was repeated on 2 March but without success. After a meager Russian bombardment, Gripenberg agreed to negotiations on 10 March. The fortress surrendered to the Russians on 18 March after a siege that had lasted roughly a month, with just one man having been wounded in action. Sveaborg (Finnish: Suomenlinna) under Admiral Carl Olof Cronstedt had been well prepared for the war with a garrison of 6,000 men, over 700 cannons, and enough stores to last until the summer of 1808. Defenses were strong enough to prevent the Russians from trying to storm the fortress by surprise. Instead the Russians laid siege against Sveaborg. The fortress surrendered on 6 May 1808 after prolonged negotiations with the Russians as the commanding officer Carl Olof Cronstedt and his council believed that resistance was futile. The Russians gained the main body of the Swedish archipelago fleet intact as well as large stores of supplies and munitions. The Russians had advanced considerably but they had also gained the long and vulnerable coastline with it. After the sea would be clear of ice there would be nothing to prevent Swedish forces from landing troops on the shore. With the Royal Navy supporting the Swedish battle fleet there was little the Russian battle fleet could accomplish. Capture of the main body of the Swedish archipelago fleet had resulted in a real advantage to the Russians since it allowed them to gain superiority in the narrow waters of the Finnish archipelago where large ships of the line could not operate. Even the powerful explosion at Sveaborg which destroyed several of the captured ships did little to change Russian superiority in the Finnish archipelago. The Russians utilized the guns from the burned ships, and from those which burned during the winter, and constructed several fortifications on the coast, both in Hangö as well as along narrow passages leading to Åbo. Under Colonel Carl Johan Adlercreutz the Swedish army counter-attacked at Siikajoki and began to halt the Russian offensive. Soon after at the Battle of Revolax (Finnish: Revonlahti), the Swedish army under Colonel Johan Adam Cronstedt started an advance towards the south. These successes yielded a promotion to Field Marshal for Wilhelm Mauritz Klingspor. The Swedish advance was very slow however, as operations were often halted due to the thaw.