HSwMS Ulla Fersen was a frigate of the Swedish Royal Navy, designed by Fredrik Henrik af Chapman, and launched in 1789.

British vessels twice detained her, once in 1798 and again in 1801, with the first event resulting in a major court case bearing on the meaning of neutrality.

The Swedish Navy tasked Captain Olof Rudolf Cederström (1764–1833) and Ulla Fersen with executing, in 1790, the first naval operation of the war.

Cederström sent in a small landing party that destroyed a battery with 49 cannons and burned down a depot of grain and naval stores.

Ommaney ordered the Swedes to permit boarding parties to inspect the merchant vessels to determine if they were carrying cargo proscribed under the British blockade and for destinations under enemy control.

[4] What is not clear from the decision is whether only one vessel was guilty of carrying potential naval stores to a destination under the blockade, or whether this was a test case for the entire convoy.

[b] Ulla Fersen was under the command of Captain Hans Hampus Fallstedt (1767–1808) and was on her way to the Swedish colony of Saint Barthelemy.

Although clearly outgunned, as Dryad carried thirty-six 18-pounder guns and eight 32-pounder carronades, which gave her a broadside of 452 pounds, Fallstedt apparently wished to escape Cederström's fate, hence the resistance and casualties.