The aged General Klercker commanded a Finnish army at Tavastehus, where Klingspor arrived with his royal orders, which were for retreat and evacuation of the country. The troops were deprived of their hopes of a battle and forced to make a retreat of nearly 600 miles, suffering from cold and hunger. The retreat continued without interruption for two months, until the army, in April, found itself between Brahestad and Uleoborg. A battle was fought at Siikajoki, April 18th, the sub-commander, General Adlercreutz, receiving instructions to make a stand against the enemy until the safety of the army supplies could be insured. After five hours of fighting, the Finns won a glorious victory over the Russians. But royal orders for a continued retreat arrived, and the Russians took possession of Siikajoki.
As long as Sveaborg, the Gibraltar of the North, was safe, the final outcome of the struggle must remain undecided. Sveaborg, the creation of Augustinus Ehrensverd, is situated on seven islets and consists of several strong works partly cut out of the rock and in an admirable way protecting and supplementing each other. The fortress was defended by 6,000 men, with 1,000 cannon and ample provisions of all kinds; in the harbor a division of the Swedish navy was at anchor. Olof Cronstedt, the commander, was dissatisfied with the king and a secret supporter of Prince Charles. His sub-commander, Jægerhorn, a brother of the leader of the Conspiracy of Anjala, was a traitor, probably in understanding with the Russians even before the war. A little army of 4,000 Russians under the command of Van Suchtelen was sent against Sveaborg. This force was too small to make a serious attack; it was not able to capture any of the fortifications; the naked rocks made it impossible to build any earthworks. What the Russians could not effect by force they accomplished by treachery, winning over the commanding officers of Sveaborg through threats and promises. When the Swedish and Finnish soldiers saw the queer behavior of their officers they planned a mutiny; but this was not carried out on account of lack of leadership. The officers tried by the most shameful lies to pacify the soldiers, Jægerhorn taking the leading part in these proceedings. Sveaborg surrendered May 3d, all Swedes being made prisoners of war, but the Finns given free leave. When the troops saw the small force of Russians and their miserable equipment they were enraged, breaking their weapons and tearing their banners to pieces. Cronstedt, Jægerhorn and the other commanding officers became Russian citizens, and received high outward distinctions; but by both Russians and Finns they were ever treated with cold contempt on account of their shameless treason.