Fredriksvern (also called Friderichsværn (1801), Frederiksværn (1865), Fredriksværen (1900) and abbreviated Frsværn) was an important Norwegian naval base, just south of Larvik in Vestfold.

Citadellet Fortress was built in the 1680s by count Ulrik Frederik Gyldenløve and had an important role during the last Nordic war from 1709 to 1720.

Fredriksvern shipyard (Fredriksværns Værft) was finished in 1750 and a number of vessels were built there, including a frigate in 1775.

It was built after the designs of naval officer and military architect Michael Johan Herbst (1699-1762), who was commander of Fredriksvern Verft.

The Common fleet had been decimated by the British robbery in 1807 and the Norwegians got the lesser share of what was left when the union was ended.