On her return in July 1780, under command of Ulrik Christian Kaas, she performed guardship duties in Øresund, off Copenhagen until 24 October 1780.

In 1801, she was equipped as a blockship and took part in the Battle of Copenhagen on 2 April 1801 where she took her place towards the northern end of the defensive line between Infødstretten and Søhesten.

[3] On 18 April 1806, Nassau was in company with Majestic, Agincourt, Dictator, Orpheus, Sparrow, and the hired armed cutter Florence captured the Prussian galliot Jonge Bartels.

On 22 March 1808 Nassau and the 64-gun Stately destroyed the last Danish ship of the line, HDMS Prinds Christian Frederik, commanded by Captain Carl Wilhelm Jessen, in a battle at Zealand Point.

[10] On the morning of 1 September 1809, Nassau was escorting a convoy of East Indiamen in the English Channel when she sighted a strange sail.

Nassau sent her boats in chase and after two hours they were able to capture the French privateer lugger Jean Bart of Saint Malo.

She was armed with four guns and had a crew of 25 men under the command of Enseigne de vaisseau Louis Ollivier Pilvesse.

In March of the next year she was commissioned as a prison ship under the command of Lieutenant William Field.