When the War started in 1914, the German Army could field 216 of these big guns, and they were used from the very first days of combat. When the Germans came upon the strong Belgian fortress of Liège, it was these guns that started the attack on August 5th, by sucessfully shelling the forts in the Eastern perimeter, and eventually paving the way for the REALLY big guns, the 42cm Dicke Berthas. It was then used with effect on all fronts, primarily in the Regiments of the Fuss-Artillerie, as one of the standard weapons of indirect fire and support. The Foot Artillery Regiments – a Corps asset – were the primary units of the heavy German Artillery, each containing two batallions of four batteries each, were the main equipment was 15cm guns. Howitzer Battallions however, had only two batteries per batallion. The number of guns per battery varied between 3 and 4. In a quiet sector, a Division had some 8-9 batteries of 15cm and 21 cm guns in support, but normally some 16 batteries were employed per division.
Experience from the fighting soon made the Artillery men realize that an increase in range would be most helpful, as the comparatively short range of the Howitzer often forced the units to site their guns well within range of most enemy artillery. A small redesign followed: the gun barrel was lengthened somewhat, from L/12 to L/14.5.
Picture: 21cm morser in action, July 1915
This new variant was called m/16 or Langer Mörser. However, as the gun already was pretty heavy and cumbersome, the redesign had been done from the premises that the weight should not be increased. That was pretty much adhered to, but with the effect that the increase in range was even less than one kilometer. Another small redesign, following combat experiences, was the fitting of a Shield. (Some m/10 were retrofitted with this, but not all.) When the war came to an end in 1918, the 21 cm Howitzers of the German Army had fired some 7 million shells.