The 21 cm SKL/40 was produced in three versions. The C/97 model was the primary
turret mounted armament of the protected cruisers. The later C/01 was the primary turret mounted armament of the
Prinz Adalbert,
Roon, and
Scharnhorst classes of armored cruisers. The
Scharnhorst class were also armed with four C/04 guns in single
casemate mounts amidships. During the First World War eight guns were removed from the
Victoria Louise-class after they were decommissioned in 1914–1915 and these formed two coastal defense batteries of four guns each. These two batteries named Freya and Hertha were stationed on the Belgian coast during the First World War. Early in the war three of the four armored cruisers of the
Prinz Adalbert and
Roon classes were lost to mines and submarines and twenty one of their spare guns were transferred to the
Imperial German Army for land use. In 1916 the guns of also became available after it was decommissioned. In 1917 one of these guns was stationed at
Cape Helles in Turkey to arm a coastal artillery unit. Seven other guns were converted to railway guns and they were referred to collectively as the 21 cm SK
"Peter Adalbert". During the Second World War these guns were reemployed by coastal artillery units of the
Wehrmacht. ==Construction==