Of the six planned bastions, only two were ready when the Swedish-Prussian war (1757-1762) interrupted the works in 1757.
The sea fortress of Svartholma was not ready, but was in defensable condition. The fortress was still not ready in 1808, when the Finnish War erupted, and two third of the guns and mortars were available. It had however been noted already in the 1760-ies, that it was not possible to place as many guns on the fortress as would be required to repulse a big attack from the sea. It had also been noted that the southern part left much to wish for.
Lovisa was the first goal of the Russians in the Finnish War (1808-1809), and the Russian main force crossed the border at Abborrfors on February 21, 1808. The Russians quickly encircled Svartholm. The Russian artillery fired sporadically at the fortress, but no serious damage was inflicted. However, the Swedish officers, led by Carl Magnus Gripenberg decided to capitulate the fortress, almost without a fight on March 18, 1808. The reasons for the capitulation are somewhat unclear but it seems like the Swedish officers didn't believe in the Swedish capability, nor the fortress' capability to withstand the Russians in this war.
As many of the other Swedish officers, Gripenberg entered Russian service after the capitulation. He was labeled a traitor in Sweden and was sentenced to death, along with other officers, for the loss of Finland. Due to a general amnesty, the death penalty process was interrupted, also for him.
Svartholma lost its strategical importance during the Russian period. It was used partly as a military base, and partly as a prison for Finnish prisoners.
The castle was largely destroyed by the British during the Crimean War on 7 July, 1855, but large parts survived the war. It continued to serve as a good harbor and a goal for weekend picnics.
The Finnish National Board of Antiquities were restoring the castle since the 1960s, and the work was finally ready in 1998.