During the Russo-Swedish War in 1788-1790 he was the Commander-in-chief of the Baltic Fleet. He won the Battle of Öland (1789), Battle of Reval and the Battle of Vyborg Bay - three brilliant victories that allowed the Russians to take prisoner 5,000 Swedish sailors and 200 officers and to bring the war to an end.
Battle of Vyborg Bay, by Ivan Aivazovsky
After the coup, which established Gustavus III with increased royal powers in 1772, the Swedish navy developed in line with Gustavus’ foreign policy ambitions. Gustavus’ direction was unclear–Russia or Denmark could be his target. The navy was important to either, but the officers of the galley fleet had been important supporters of Gustavus’ coup. New rules and organization were established in 1773. A royal inspection in 1775 led to the College of Admiralty moving from Karlskrona to Stockholm in 1776, to be closer to the court. The officer corps was reformed to make professional competence more significant in promotion. In 1781 the famous ship constructor, Fredric Henrick af Chapman (1721–1808), was appointed Director of Naval Construction at Karlskrona. Chapman had extensive theoretical knowledge of engineering sciences and since the 1760s had been designing and building vessels for inshore operations. In 1780 he was co-author of the plan approved by Gustavus for a new sailing fleet of battleships and frigates. Under his supervision, Karlskrona became one of the most extensive and modern yards in Europe.
The impact of Gustavus’ reforms are still a matter of debate, but by the summer of 1788 Gustavus was ready to attack Russia. While an army advanced through Finland and another, with the archipelago flotilla, was to move along the coast into the Gulf of Finland, a third army with the sailing fleet was to attack Kronstadt and land the army at Orainenbaum to advance on St Petersburg. The Russian fleet of 17 line under Admiral Greig met the Swedes, also with 17 line, off Suursaari island (Battle of Hogland) on 17 July. The battle was fought in line and after seven hours, the Swedes broke away in the darkness. Greig had done enough to avert the Swedish landing. Over the winter, Russian building of gunboats for its archipelago flotilla outstripped the Swedes. An action off Öland on 25 July 1789 between two evenly matched battlefleets was again indecisive, but the archipelago flotillas met in a decisive action just one month later on 24 August (Battle of Svensksund). Vice Admiral Nassau-Siegen decisively defeated the Swedish inshore flotilla. Swedish attempts to revive the plan of attack against Kronstadt in 1790 foundered in an indecisive attack on Tallinn in May, and a further attack on Russian battleships failed. Gustavus’ mistakes allowed the Russian sailing fleet to blockade his sailing and archipelago fleets in Vibourg Bay. On 3 July the Swedish sailing ships broke out and Gustavus was able to take the inshore fleet to Svenskrund. An impetuous attack on the Swedes on 8 July ended in disaster for the Russians. The peace treaty restored the boundaries to the status quo ante bellum. Both sides had shown that seapower–exercised by a combined force of battleships, cruisers and inshore craft–were critical to the projection of land power in the eastern Baltic, but both had also shown that their defensive capabilities far outweighed their offensive power. Russia remained a powerful force in the eastern Baltic, but not so powerful as to pose a vital threat to the interests of the other powers in the region. While the coasts of the Baltic remained open to traffic, and Russia remained prepared to trade its vital naval stores, it was in no one’s interest to become bogged down in a war that was so well suited to defence.
On 17 July 1788, the Swedish fleet of 20 ships (1,180 guns) under the command of Duke Carl engaged the Russian force of 17 ships (1,220 guns) under Admiral Greig off the island of Hogland. Tactically, the Battle of Hogland was a draw, with each side losing a ship. The Swedes suffered 130 killed and 334 wounded while inflicting 321 killed and 702 wounded upon the Russians. Strategically, the Russians emerged with the advantage as their forces continued to command the Gulf of Finland, thereby enabling them to regroup while frustrating the Swedish plans against St. Petersburg. Moreover, with his forces still intact, Greig disposed his forces at Hangö and Porkkala to cut Swedish communications between Stockholm and Sveaborg.
By the end of August 1788 the war had expanded to include the kingdom of Denmark-Norway. Under Russian pressure, Denmark-Norway joined as an auxiliary power and pledged a force of 6 ships of the line, 3 frigates, and 12,000 men against Sweden.
During the winter of 1788–1789 the Swedish fleet, consisting of 21 ships of the line, was concentrated at Karlskrona. The Russian fleet, although larger, was spread out, with 11 ships of the line at Copenhagen, 10 at Revel, and 14 at Kronstadt. However, with a massive construction effort at St. Petersburg between fall 1788 and spring 1789, the Russians expanded their flotilla to over 150 vessels.
On 13 July 1789, Admiral Vasili Tchitchagov sailed from Revel toward Karlskrona with a Russian force of 20 ships of the line, 6 frigates, and 19 smaller warships. Meanwhile, another Russian force under Admiral Temofey Gavrelovitch Koslanianov was south of Copenhagen with 11 ships of the line, 4 frigates, and 3 smaller ships. The Danes supported Koslanianov with a contingent of 11 ships of the line and 3 frigates.
When word reached Tchitchagov that the Swedes had been sighted south of Öland, he called for Koslanianov to join him there. On 26 July 1789 the Swedes struck Tchitchagov off Öland before the two Russian fleets could unite. Duke Carl had 29 ships at his disposal. Once again the battle was indecisive. Afterward Koslanianov managed to effect the union with Tchitchagov on 1 August. On 6 August Tchitchagov ordered the combined Russian fleets back to Russia instead of trying for a decisive victory.
The naval engagements of 1790 produced still more split decisions. The Russians hoped to concentrate all their forces for a united assault on the two Swedish fleets in Viborg Bay. For their part, the Swedes still sought to press on and capture St. Petersburg. On 2–4 July the Swedes lost a third of their ships of the line while breaking out of the Gulf of Viipuri in the Battle of Viborg Bay. However, the following week the Swedish galley fleet scored a resounding victory over the Russians on 9 July at the Second Battle of Svenskund. The Swedes destroyed 52 Russian craft at the cost of only 6 of their own. The Peace of Värälä, signed on 14 August 1790, concluded the war with no territorial changes.
Overall, the war elevated Russian preponderance over Sweden in the Baltic. During the three years of war, Sweden lost 12 ships of the line and gained 1, whereas the Russians lost 4 and gained 6 without counting new construction. By war’s end Russia possessed 46 ships of the line, exclusive of the Black Sea Fleet, compared to 16 for Sweden. Russia and Sweden would find common cause against the French Revolution and would form a defensive pact in fall 1791.