Sturmpanzer I ' Bison'

The 15 cm sIG 33 (Sf) auf Panzerkampfwagen I Ausf. B, commonly but unofficially referred to in postwar literature as the Sturmpanzer I "Bison", represents one of the earliest German attempts to provide mobile heavy infantry support during the opening phases of the Second World War.

The origins of the vehicle trace directly to the performance of the 15 cm schweres Infanteriegeschütz 33 (heavy infantry gun Model 33) during the invasion of Poland. Although the sIG 33 proved highly effective as a direct-fire weapon against fortifications, bunkers, and enemy strongpoints—firing a 38 kg high-explosive shell to ranges of approximately 4.7 km—its towed configuration severely hampered mobility.

In response, the Waffenprüfung 6 (Weapons Testing Office 6) issued a requirement in late 1939 for a self-propelled variant. Initial conceptual designs envisioned a purpose-built tracked carriage, but wartime resource constraints and the availability of obsolete Panzer I Ausf. B chassis—already being phased out of frontline tank service—dictated a simpler expedient solution. The firm Alkett (Altmärkische Kettenwerke) in Berlin-Spandau undertook the conversion, retaining the original gun carriage and wheels while fabricating a rudimentary armored superstructure. The turret was removed, and a tall, open-topped, three-sided armored box (primarily 13 mm plates, with some sections as thin as 4–10 mm) was erected forward. The sIG 33 howitzer was mounted unmodified, complete with its wheels housed in metal cradles. Production commenced in February 1940, yielding 38 vehicles (including one prototype) by March of that year.

They first saw action during the May–June 1940 campaign in the West (France), where they provided effective support against fortified positions. Reports from the 702nd Company alone credited the vehicles with destroying 24 bunkers, 31 guns, 13 anti-tank guns, and six tanks. Subsequent operations included the April 1941 invasion of Yugoslavia and Greece. On the Eastern Front from June 1941 onward, the Bison-equipped companies participated in Operation Barbarossa and subsequent advances. By mid-1943, attrition through mechanical failure, enemy action, and operational wear had reduced the fleet significantly; the last recorded operational examples belonged to the 704th Company with the 5th Panzer Division as of June 30, 1943.

Despite its conceptual promise, the vehicle suffered from profound limitations. The Panzer I chassis, already outdated and underpowered, proved severely overburdened, leading to chronic mechanical failures—particularly in the transmission, brakes, suspension, and tracks (with breakdowns reported as high as 60% during marches). The high silhouette (up to 3.35 m) and minimal armor rendered it vulnerable to even small-caliber weapons, artillery fragments, and anti-tank fire; the open-topped and open-rear design exposed the crew to weather, shrapnel, and small-arms fire. Ammunition scarcity forced constant dependence on vulnerable supply columns.

The 15 cm sIG 33 (Sf) auf Panzerkampfwagen I Ausf. B was an interim solution born of necessity, successfully bridging the gap between towed artillery and mechanized warfare in the early, triumphant campaigns of the Wehrmacht. Yet its reliance on an inadequate chassis, combined with inadequate protection and logistical vulnerabilities, ultimately condemned it to obsolescence by 1943.