The 120-mm Heavy Artillery Battery on Landsort, a Cold War military

Landsort 120-mm. Heavy Artillery Battery, located on Öja outside Nynäshamn, was built to protect Stockholm from a Soviet attack during the Cold War. The construction began as part of the Havsbandslinjen, a chain of artillery batteries started around 1936, to protect Stockholm and eastern Sweden. However, this chain of batteries was abandoned by the 1960s, replaced by the ERSTA batteries. Landsort 120-mm. Heavy Artillery Battery is a member of the latter group, operational from 1977 to 1990.

It is one of five similar installations along the Baltic coast, all but one (the one on Landsort) were dismantled after the 2000 defense decision. Since 2018, the battery is a national monument. The 120-mm Heavy Artillery Battery at Landsort features a gigantic 150-ton Bofors cannon, model 12 cm tornautomatpjäs m/70. It can fire 22-kilogram projectiles, one every second, to targets up to 30 kilometers out at sea. The soldiers' quarters remain bedded and the technical equipment is entirely of Swedish origin and is roughly 1970s standard but was world-leading technology and was exported. The battery is open to the public as a museum since January 1, 2013, called Batteri Landsort.

Sources: Wikipedia, OpenStreetMap, Wikidata, Wikimedia Commons