The cannons had been constructed in 1934 and was planned used on a huge "H" Class battleship but it was never built.
The barrels are approximately 20 meter long and could fire shells up to a distance of 56 Kilometres. The guns could fire three different shells, High Explosive, High Explosive/Armour Piercing (both ca 1030 kg) and the special long range shells called the "Adolf Grenades" (ca 600 kg). The fire rate was 2 shells pr minute. Each shot would take with it 40 kg steel from the barrel so totally it would be able to fire 250-300 rounds. This batterie was never fired at enemies, but has been test fired several times, the last time in 1957.
Today one of the guns is open for the public, but only through guided tours as it is located inside an operative military base. We visited the gun and had a two hours tour through the bunker and the turret "Barbara" which is kept operative for museal purposes. I highly reccommend visiting this place if you are in Northern Norway as it is a spectacular site.