Karjohansvern (Karljohansvern Orlogsstasjon, KJV) in Horten was the main base for the Royal Norwegian Navy from 1819 to 1963.
It was first called Hortens verft, and later Marinens Hovedværft until King Oscar I named it Carljohansværn værft in 1854 (after his father Karl Johan). It was the site of the Navy Main Yard, Navy Air Plane Factory, Navy Museum, Navy Schools and the forts Norske Løve and Citadellet.
Naval District East (ØSD) based there was disbanded in 2002. The Museum, the Royal Norwegian Navy Band, a department of the Norwegian Defence Research Establishment and some of the Navy's school administration is still present. As of 2006 the entire base including 73 buildings has been given protected heritage status by the Directorate for Cultural Heritage in Norway. Karljohansvern is open to the public. Only Vealøs is still owned by the Department of Defence.