One of its most distinctive features is its original design, consisting of a separate shipbuilding area inside the yard and a area with houses and a school outside the yard.
The establishment of Karljohansvern was controversial right from the outset, and its construction in the 19th century was interrupted many times. In the early years, building activity was concentrated around the slips and comprised simple sheds and wooden buildings.
From 1829 until 1850, several magnificent Empire-style buildings were built. The most important buildings that still stand are one of the big storage buildings and the two barrack quarters with outbuildings. The buildings from after 1850 are in a more romantic style, with an architecture inspired by historicism in undressed brick. The best examples are Norske Løve fort at Vealøs, the yard gate, the drill house and the church. In addition to the grander buildings, there are are several utility buildings built in brick and with a simpler design, including workshops and fireproof storerooms.
Although the naval base was a military facility, it was not given a traditional fortification design. The building process took a long time, and it took place during a period when the assumptions on which the building of urban fortifications were based were constantly changing as a result of new weapons technology and new theories about defence methods.
As a naval base, the facility usually had a substantial defensive capacity, also in the form of heavily armoured vessels. The first major development in the 1850s was based on smooth-bored cannons and it therefore almost immediately became outdated. As a whole, the facility has a somewhat unfinished and diffuse appearance as a result of the constantly changing plans. However, it does contain several well-known features that are characteristic of traditional 19th century fortifications architecture.
Today, the fortifications consist of several elements from the period from the 1850s to the 1870s. The most characteristic feature is in the northernmost part of the area: Norsk Løve fort (1859) is a small and compact brick and granite facility in which the 'envelope' forms a closed circle for 22 cannons and is surrounded by a dry moat and sloping bulwark. The other fortifications consist of three cannon emplacements in the north, east and south-east of the area (at Møringa-, Tivoli- and Hortenstangen) dating from the 1870s.
The navy's main base was transferred to Bergen in 1963, but there was still extensive military activity here until the end of the 20th century. The Armed Forces still have a presence at Karljohansvern, but on a much smaller scale than before. The yard and a number of the buildings have been sold for civil use, which now has a more and more dominant place at this former military establishment.