28 cm SK L / 40 gun The 28 cm SK L / 40 was a German naval gun that was used in World War I and World War II by all German pre - dreadnought battleship s . It was the first large German naval gun to use a horizontal sliding block breech design rather than the interrupted screw more commonly used in guns of this size ; it was also the last large German naval gun to load all its propellant in a single case . It was adapted for land service after the pre - dreadnoughts began to be disarmed beginning in 1916 . Four guns served on coast defense duties on the island of Wangerooge during World War I on fixed mounts . During World War II these guns were transferred to Brest . Others were used in railway mountings in both World Wars . Description . The 28 cm SK L / 40 gun weighed , had an overall length of and its bore length was . Although designated as , its actual caliber was . Early guns , possibly designated as the 28 cm K L / 40 , were built using the older hoop method of construction , but later guns used more modern built - up techniques with an inner gun tube and several outer jackets . It was the first large German naval gun to use Krupp ' s horizontal sliding block , or " wedge " , as it is sometimes referred to , breech design rather than the interrupted screw used commonly used in heavy guns of other nations . This required that the propellant charge be loaded in a metal case ( usually brass ) which provides obduration – it seals the breech to prevent escape of the expanding propellant gas . The 28 cm SK L / 40 was the last large German naval gun to load all its propellant in a single case ; later guns required a fore charge in addition to the main charge in the cartridge case . < ref name = " NavWeaps ( 28 cm / 40 ) " > < / ref > Naval turrets . These guns were used in twin gun turret s as the main armament of the - and pre - dreadnoughts . The Drh . L . C / 01 turret was used by the " Braunschweig " - and " Deutschland " - class battleships , one twin gun turret at each end . Its guns could depress 4° and elevate 30° and could traverse about 150° on either side of the centerline . It could fire a L / 2 . 6 armor - piercing shell to a maximum range of at maximum elevation . These ships stowed 85 rounds per gun . The rate of fire for both types of turrets was about 2 rounds per minute . Land mountings . Beginning in 1916 some guns were adapted for use ashore . One obvious change made for land service was the placement of a large counterweight just forward of the trunnion s to counteract the preponderance of weight towards the breech . This , although heavy , was simpler than adding equilibrators to perform the same function . It was fitted with a hydro - pneumatic system to absorb the recoil from firing and to return the gun to its firing position , ready for the next round . The first four guns were placed in " Bettungsschiessgerüst " ( firing platform ) ( BSG ) mountings in 1917 for coast defense duties as part of " Batterie Graf Spee " on the island of Wangerooge . These were a semi - portable mount that could be emplaced anywhere after several weeks of labor to prepare the position . It rotated on a pivot at the front of the mount and the rear was supported by rollers resting on a semicircular rail and was sometimes equipped with a gun shield . The gun ' s rate of fire in these mounts was about one round per five minutes . Other guns from the battleships were put on railroad mountings as the 28 cm SK L / 40 " Bruno " and used as railway gun s . Ammunition . Before and during World War I , the gun used about of RP C / 12 ( " Rohr - Pulver " – tube powder ) propellant that was a mix of nitrocellulose , nitroglycerin and small amounts of other additives with a calorific value of 950 and an uncooled explosion temperature of 2975 kelvin s . In World War II , it was replaced by RP C / 38 that substituted diethylene glucol dinitrite for the nitroglycerine which had a calorific value of 810 and an uncooled explosion temperature of 2495 K . This had the virtue of being harder to ignite , lessening the risk of a catastrophic fire or explosion , and reduced the erosive effects of the gaseous propellant on the gun ' s bore . Sources differ on the amount of RP C / 38 used by the gun during World War II ; Campbell says , but Hogg says . These guns mounted fired two types of shells during World War I : armor - piercing ( AP ) L / 2 . 6 and high explosive ( HE ) L / 2 . 9 types . During World War II , the guns fired a wider variety of shells , including high explosive L / 2 . 9 , L / 4 . 3 , and L / 4 . 1 shells and a heavy HE L / 4 . 4 projectile ; the AP and HE rounds weighed , while the heavy projectile weighed . Due to the greater elevation available in the BSG mount , the " Sprgr L / 4 . 4 m . Bdz . u . Kz . ( mit Haube ) " had a maximum range of . Armor penetration . One source credits the " Pzgr L / 2 . 6 " shell with the ability to penetrate of side armor at . History . Naval guns . The Treaty of Versailles allowed the Germans to retain four pre - dreadnoughts , although only two , and , were rearmed with their original 28 cm SK L / 40 guns . The former fired the first shots of World War II when she began bombarding Polish defenses on the Westerplatte on 1 September 1939 while the latter also participated in the Polish Campaign . However both ships were relegated to training duties shortly afterwards . Coast defense guns . Some of the 28 cm SK L / 40 guns were transferred to the German Army from the Navy ( Kaiserliche Marine ) when the pre - dreadnoughts began to be disarmed and relegated to training duties in 1916 after the Battle of Jutland had proved that they were not suitable for contemporary naval combat . The first four guns , formerly used on , were placed in BSG mountings in 1917 for coast defense duty as part of " Batterie Graf Spee " on the island of Wangerooge . During World War II only seven guns were used on as coast defense duties on BSG mountings . The four guns of " Batterie Graf Spee " had survived World War I and were transferred to Brest , France in 1940 . Railway guns . Approximately twenty other guns from the battleships were put on railroad mountings as the 28 cm SK L / 40 " Bruno " and used as railway gun s . A number were kept by the Kaiserliche Marine and used on coastal defense duties , but the others were used by the Heer in more traditional roles as long - range heavy artillery . Surviving weapons were used by the Germans in World War II as coast defense duties .