15cm sIG 33 (Schweres Infanterie Geschutz 33) 150mm Towed Heavy Infantry Gun
The serviceable 15cm sIG 33 Heavy Infantry Gun was developed and adopted in Germany during the rearmament period of the 1930s.
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The German Army fielded all manner of artillery during World War 2 (1939-1945) - field guns, howitzers, railguns, and infantry-level support guns. For the latter, the standardized system became the 15cm sIG 33 ("Schweres Infanterie Geschutz 33") series gun introduced during the German rearmament period of the 1930s. Total production of the gun numbered approximately 4,600 units before the end of the fighting in 1945.
Design work on the new infantry gun spanned from 1927 to 1933 with Rheinmetall charged with its production in 1936. Eventually AEG-Fabriken and Bohemisch Waffenfabrik participated to shore up the wartime requirement. The sIG 33 utilized a considerably large caliber (150mm) for an infantry-level weapon and its weight was anything but favorable in terms of mobility. In its original form, the type was seen with a pair of solid, multi-spoked wooden wheels set on the box trail carriage assembly. The gun tube featured a horizontal sliding breech block and hydropneumatic recoil mechanism. The mounting hardware allowed for an elevation span of 0 to +73 degrees and traversal of 11.5 degrees from centerline. Fitted sights were the Rblf36 series. A thin gun shield was intended to protect the gunnery crew from battlefield dangers but its overall protection was minimal at best.
In time, it was decided to rework the carriage and incorporate a multi-spoked steel wheel design approach which fitted rubber tires. This was better for service concerning the new mechanized approach to mobile warfare where high-speed road travel was replacing the old, tried-and-true horse-drawn artillery piece. The shift in material only made the weapon heavier and more cumbersome in but it nonetheless became a more modern field piece.
By the end of the decade, still another approach was enacted in which lighter weight alloys were incorporated in place of all-steel. While this made for a more manageable weapon system, it took vital wartime resources away from other critical programs and production of this sounder gun was only in the hundreds before factories began reverting back to manufacture of the original arrangement. An all-alloy carriage under consideration in 1939 but this development was not adopted.
In practice, as was the case with most of the German guns of the war, the 15cm sIG 33 gave good service for its role. Its field weight totaled 4,000 pounds and its dimensions included a length of 4.4 meters and a width of 2 meters. Its relatively compact size allowed for it to be hauled relatively easily by mover vehicle or "beast of burden" and transportation by rail provided few issues. The weapon's listed rate-of-fire was up to three rounds-per-minute out to effective ranges of 5,100 yards (4,700 meters). Muzzle velocity was 790 feet per second.
The sIG 33 fired a conventional, fin-stabilized HE (High-Explosive) shell known as the "I Gr 33". When loaded into the gun tube, the projectile protruded some from the barrel as the propellant charge and a driving rod was set down the tube prior to the shell being inserted into the weapon (the rod fell off during the projectile's flight). Each shells weighed about 84 pounds and carried a filler compound of amatol. This standard HE projectile was followed by the "I Gr 38 Nb" smoke round and the I Gr 39 HI/A hollow-charge round. The Stielgranate 42 projectile was used as a demolition round for obstacle clearance and had 60 lb of amatol as its filling compound - of course there was no restriction for its use against concentrations of dug in enemy troops.
15cm sIG 33 systems fought on in a variety of battlefield roles into the last days of 1945 - leading up to the German surrender of May. This same gun was featured on the sIG 33 Self-Propelled Artillery (SPA) vehicle of which 370 were built between 1939 and 1944. This development was in response to the poor mobility of the sIG 33 piece showcased during the Polish Campaign of 1939. The chassis of the Panzer I light tank formed the foundation of this new vehicle before focus switched to the Panzer II light tank hulls. Then followed similar versions based on the Panzer 38(t) light tank and then the Panzer III medium tank.