The hemmema was a specialized vessel for use in the shallow waters and narrow passages that surround the thousands of islands and islets extending from the Swedish capital of Stockholm into the Gulf of Finland.
Compared to galleys, the hemmema had a deeper draft and was slower under oars, but offered superior accommodation for the crew, carried more stores, was more seaworthy and had roughly ten times as many heavy guns.
The Swedes began to deploy inshore flotillas of shallow-draft vessels, beginning with smaller versions of the traditional Mediterranean galleys.
For two decades, the struggle for power between the Hats and the Caps, the dominant political factions at the time, and rivalries between army and navy brought about changes to the archipelago fleet.
The parliamentary victory of the Hats in the Riksdag in 1769–70 and the coup d'ètat by King Gustav III in 1772 secured the archipelago fleet's status as an independent branch of the army.
The Swedish armed forces invested considerable resources in the new army branch and made it a professional, independent organization.
The archipelago fleet attracted members of the social and cultural elite who enjoyed the protection and patronage of King Gustav III, who had established himself as an absolute monarch in the 1772 coup.
[5] Augustin Ehrensvärd argued for new archipelago vessels that combined firepower, maneuverability, seaworthiness, and decent crew accommodations.
[6] Chapman specifically designed the archipelago frigates for service off the south coast of Finland and named them after the Finnish provinces of Uusimaa, Pohjanmaa (Österbotten), Turunmaa (Åboland), and Hämeenmaa (Tavastia).
[10] Chapman's archipelago frigates provided better protection for their crew than the galleys they replaced, and up to three times the capacity for stores and provisions.
The new ship types also increased the archipelago fleet's firepower, provided it with better defensive capabilities, and made possible more efficient fire support in amphibious operations.
[15] The addition of diagonal bracers to reinforce the hull allowed the later hemmemas to carry guns more powerful even than those on the largest sailing frigates of the high seas navy.
[16] Due to their considerable firepower and relative size, naval historian Jan Glete has described the hemmemas as "super archipelago frigates".
[21] Birger Jarl sank in an accident in 1813[22] and Erik Segersäll was planned for conversion as a paddlewheel steam battery for coastal defense, though the idea was eventually abandoned and the ship scrapped in 1826.
Although it had superior firepower relative to galleys, its sailing qualities were somewhat mediocre and while highly manoeuvrable under oars, it was still difficult to propel while rowed.
[23] A hemmema had the potential to be an effective weapon against galleys, matching their forward firepower and severely outgunning them with its broadside armament.
Inside an enemy galley formation, it could wreak considerable havoc, but such a maneuver was never achieved in an actual battle, leaving that tactical role untested.
The Swedish hemmemas were all built to the same specifications, except for the early design Oden, and Birger Jarl and Erik Segersäll carried heavier armament than the others.