10.5 cm tornautomatpjäs m/50

In 1949 the Inspector of the Coastal Artillery (IKA) ordered an investigation concerning the replacement of numerous older, and for the most part, completely obsolete artillery system with model years stretching as far back as the late 1800s. Most of these had been hastily built during World War II using old naval guns in very simple emplacements which were not designed with endurance and high survivability in mind. Protection from nuclear weapons was non-existing and collective BC protection was very limited usually requiring most of the gun crews to wear gas masks. Finally, most of the older guns were 57 mm designs and lacked the firepower to be an effective defense against an invasion.
In 1950 Bofors offered 6 fully automatic 105 mm guns (probably based on an earlier naval dual-purpose gun design) in armored turrets, to be delivered in 1953-54. However, various problems at Bofors caused the delivery to be delayed until late 1957. One of the guns (which ended up becoming Gun #2 at Nåttarö) also had its breech damaged somewhere in the process. This was repaired and the gun delivered anyway.
All of the guns went to the Stockholm area where the need to replace older systems was deemed the most urgent.

The 6 guns were split into 3 batteries consisting of 2 guns each. They were built in such a way that each gun in a battery could be targeted individually, that is, the battery's fire could be split between two targets. Each gun emplacement was designed to be completely self-sufficient and in the case of Battery Arholma they were spread across 2 islands.

• Arholma, 1960: A fire in a storage shed seriously damaged the parts for turret #2, designated for Ovanskär. This delayed its installation with several years.
• Nåttarö, 1960s: Gun #1 malfunctioned several times due to premature wear of various parts and other technical problems.
• Nåttarö, 1984: An explosion occurred in turret #2. One man was killed instantly while 4 others suffered burns but survived. The subsequent investigation concluded that the firing system malfunctioned in such a way that it allowed the gun to fire before the breech had fully closed, thus causing much of the propellant gases to enter the magazine spaces below. The turret was repaired and returned to service.

When the 10.5/50 system was first designed and built its nuclear protection was thought to be pretty good, based on the knowledge concerning the effects of nuclear weapons available at the time. However, as more research became available, the protection of most parts of the system had to be downrated quite a bit. Nevertheless, 10.5/50 was a highly effective weapon system mainly owing to its very high rate of fire which meant a large volume of ammunition could be placed on a target.
In the 1980s, when the coastal artillery decided not to use the option to order more 12/70 systems the fire control systems meant for those installations were redirected to replace older systems. This meant that all 10.5/50 installations received a modern ArtE 724 digital fire control system, complete with the new HSRR fortified radar system and AML 702 laser rangefinder and low-light TV system. The installations were also updated with new communications including the STRIKA 85 computerized command and control system, as well as a general renovation of the accommodation spaces.
A decision in 1999 meant that all coastal artillery systems would be disbanded in line with the Swedish government's new take on defense. The 10.5/50 installations were dismantled in the early 2000s, with only Arholma 1 being retained as a State Construction Memorial. It opened as a museum for the 2008 season and is mostly open during the summer, but may be visited any time of the year by groups if booked in advance.

• https://arholmanord.se/batteri/ Battery Arholma information and museum (in Swedish)