The ERSTA study

The ERSTA study was a 1960s Swedish coastal defense study aimed at determining what would become the next heavy coastal defense system. A 120 mm automatic gun system was eventually selected.

Rb 08 anti-ship missile installations were seriously considered but abandoned, possibly because much of that project may have been exposed to the Soviet Union by Stig Wennerström, the spy who also leaked vital information about the air defense system STRIL 60.

Deployment

Several locations were studied and suggested for 12/70 batteries, and 10 locations were eventually selected and constructed in two series. In the end, due to funding issues, only the first series of six batteries was built starting in 1971. Additional cost-cutting measures had to be taken so EMP protection was severely reduced and the supporting installation of each gun was made smaller by replacing the full featured kitchen with a less capable galley and reducing the overall size of the crew quarters.

Turret and gun system

The 12/70 gun is a fully automatic, water-cooled vertical sliding wedge design mounted in an armored turret which is electrically traversed under computer control while the elevation motor is controlled manually (presumably a cost-cutting measure). It is fed from a magazine several meters below ground where the crew uses special air-cushion carts to feed cartridges onto a loading table. From the loading table the cartridge is fed through a hoist system and loaded into the gun using a pendulum loader. Spent cartridges are passed down a chute into a space at the bottom of the gun well, which is over 18 m (59 ft) deep on tapj 9101 and a few meters less on tapj 9102. The turret is manned by three men (gun commander, traverse operator and elevation operator) with the rest of the gun crew working in the magazine or the installation below.

To protect the gun system from ground shockwaves and overpressure in case of a nuclear detonation, the barrel is lowered into its storage position in a special "ground attachment fork" and the turret is hydraulically lowered and anchored to its foundation. The muzzle is automatically sealed when the barrel is lowered into storage position. During a nuclear attack, the turret crew may not stay in the turret because of the initial radiation, but they may reoccupy it and be ready to fight immediately after the attack thanks to a special liner which reduces induced radiation to such a point that it is safe to immediately reoccupy the turret.

Supporting installation

Each gun emplacement is supported by an installation which contains power supply, accommodation and a galley. This enables at least 60 days endurance when cut off from the outside world. It consists of a steel-framed structure placed on rubber cushions for protection from ground shockwaves. On a type 9101 emplacement, this installation is a 3-story structure placed below the magazine.

The command and control center is a larger installation consisting of a 5-story building of a similar design which also has a more capable kitchen and a sickbay with surgery capability. In addition to cables and ordinary radio masts, the 12/70 command features reserve masts which are normally stored in silos below ground and may be raised as needed.

Fire control

The 12/70 system marked the first use of the ArtE 724 digital fire control system. This may be fed information from several type of ranging stations, chiefly a radar system called HSRR which consists of a radar antenna normally stored below ground under an armored hatch. At least two surveillance radars are attached to the battery, and when a target is detected the HSRR may be raised and used for ranging reducing the time it is exposed above ground.

The other main ranging instrument is a laser rangefinder called AML 702 installed along with a low-light TV camera in an armored turret called the "laser eye". This can be remote controlled from the ranging station or command center and takes the place of the periscopes used in older installations.