The increased tension in Europe in the late 1930s forced many nations to accelerate development of new armoured vehicles. This also applied to the cause of that tension: Germany. The war was inevitable, and the offensive power of the army grew day by day.
Meanwhile, European countries, including France, Czechoslovakia, and Belgium concentrated their efforts on defensive measures. One of those measures was fortifications. The Maginot line is the most famous of them. In 1936, Czechoslovakia began building a defensive perimeter known as the Beneš line. It included an impressive 250 bunkers and almost 10,000 light fortifications. The Belgian KW line was even more impressive. The upcoming blitzkrieg wouldn't be a walk in the park, at least in theory.
The Germans didn't sit on their hands either. In 1938, the German army reclassified the Flak 18 88 mm AA gun into a dual purpose weapon. Now they would be also used against fortifications and tanks. Special units to combat enemy fortifications were hurriedly formed. It became obvious that towed guns protected by only a gun shield were inadequate for this task. A logical solution was to launch a program to develop a special SPG.
This gun was selected as the weapon for the SPG. During the design stage, it became obvious that the artillery system will have to be redesigned. The problem was that there wasn't a wide choice of chassis available for such a large gun, and the requirements for the internal layout were unyielding.
The gun was altered significantly for this purpose. For starters, a massive two-chamber muzzle brake was added. The gases it emitted raised a cloud of dust and revealed the position of the SPG, but the recoil length was significantly shortened. The barrel also became segmented.