The 15cm Schweres Infanteriegeschuetz 33/1 auf Panzerkampfwagen 38(t), often called the SdKfz 138/1 "Grille", German for "Cricket", and sometimes referred to as the Bison, was a self-propelled artillery piece that was used by Germany during World War II.
The Grille was a self-propelled gun built on the chassis of the Panzer 38(t). The turret of the original tank was removed and replaced by a superstructure, which mounted the howitzer and fighting compartment.
The new superstructure featured a protective shield that provided cover for the otherwise exposed crew. The shield wrapped around the entire fighting compartment, with its front plate being taller than its rear. The sides of the shield slowly inclined down as they reached the lower rear plate, connecting the two components. This left very little movement capabilities for the main gun. To attack a new target, the entire vehicle had to turn in the intended direction.
The vehicle's main advantage was its mobility. Unlike standard towed artillery pieces, the Grille was powered by a 147 h Praga EPA/2 engine capable of moving it at speeds of up to 22 mph. The Grille could also fire at any time, it had no need to be stopped and emplaced.
The German SPG was crewed by five tank men, four of which were located near the gun in the fighting compartment and a fifth in the forwards driver position. It featured a FuG 16 radio for communicating with other German forces.
The initial prototype for the Grille was completed at BMM in 1942. In response, the SdKfz 138/1 Ausf. H began production in February of 1943. At almost the same time, production for the Ausf. M version began in April 1943. The models were mainly produced by BMM, the Czech factory that produced most variants of the Panzer 38(t). The original plans called for 200 Grille tanks; 90 on the Ausf. H chassis and 110 on the Ausf. M. The Ausf. M, however, continued production well into 1944, far beyond the original goal. In total, about about 500 Grilles were produced.
The Ausf. H Grilles were attached to numerous units stationed in France and Poland, including divisions of Panzers and Panzergrenadiers. They were used again in Italy, North Africa, and the Soviet Union in 1943. A small few were kept garrisoned with 2. Panzer-Division in Normandy, and saw action at D-Day.
The later rear-cabined Ausf. M Grilles were issued to a large amount of "Schwere Infanteriegeschütz" (German: Heavy Infantry-Gun) companies in the mainline Wehrmacht, and saw plentiful action on all fronts until the end of the war in 1945.
15cm sIG 33/1(SF) auf PzKpfw 38(t) Ausf. H: The initial version built on the Panzer 38(t) Ausf. H chassis. The engine was located in the back, with the shield gun mounted in the middle. 
15cm sIG 33/1(SF) auf PzKpfw 38(t) Ausf. M: A version based on the Panzer 38(t) Ausf. M. The engine was placed in the middle of the vehicle and the gun mount was moved to the rear of the hull. The Ausf. M had the same gun, engine, and suspension as the Ausf. H.
- Encyclopedia of German Tanks of World War Two, Peter Chamberlain and Hilary Doyle, 1999
- Rickard, J (8 August 2013), Grille/ 15cm sIG33 (Sfl) auf PzKpfw 38(t) ausf H, M , http://www.historyofwar.org/articles/weapons_grille.html