Karjohansvern was the main base for the Royal Norwegian Navy from 1819 to 1963. It was the site of the Navy Main Yard, Navy Air Plane Factory, Navy Museum, Navy Schools and the forts Norske Løve andCitadellet.
Naval District East (ØSD) based there was disbanded in 2002. The Museum, the Royal Norwegian Navy Band, a department of theNorwegian 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.References:
First record of Kastelholma (or Kastelholm) castle is from the year 1388 in the contract of Queen Margaret I of Denmark, where a large portion of the inheritance of Bo Jonsson Grip was given to the queen. The heyday of the castle was in the 15th and 16th centuries when it was administrated by Danish and Swedish kings and stewards of the realms. Kastelhoma was expanded and enhanced several times.
In the end of 16th century castle was owned by the previous queen Catherine Jagellon (Stenbock), an enemy of the King of Sweden Eric XIV. King Eric conquered Kastelholma in 1599 and all defending officers were taken to Turku and executed. The castle was damaged under the siege and it took 30 years to renovate it.
In 1634 Åland was joined with the County of Åbo and Björneborg and Kastelholma lost its administrative status.