German engineers invented the "self propelled gun mount" class of artillery. The first work in this area was done during WWI, but it truly became a mass event 25 years after it ended. The recipe was simple: take a light or medium tank and use its parts to to build a chassis with bulletproof armour. A slightly modified version of a towed gun was installed on that chassis. Thanks to this phenomenon, the mobility of German artillery grew significantly. The Hummel became the post powerful of German "self propelled gun mounts". This SPG earned its position as one of the symbols of German self propelled artillery.
A Union of Competitors
Krupp was the center of medium SPGs in 1942. Work on this type of vehicle began in Hessen before WWII. The results were complicated. The 10.5 cm K. L/52 Selbstfahrlafette, envisioned as a bunker buster, turned into the Pz.Sfl.IVa, nicknamed Dicker Max. The name was no accident. With a mass of 22 tons, the SPG only carried a 180 hp engine. The vehicle, reclassified as a tank destroyer, was not great in terms of mobility. For a number of reasons, mass production of these vehicles, finally renamed Pz.Sfl.IV (10 cm), was cancelled at the end of 1941.
Things were going much better with another SPG that branched off the 10.5 cm K. L/52 Selbstfahrlafette project. It first carried the name Pz.Sfl.IV (leFH 18), but later the name changed to Pz.Sfl.IVb. It had six wheels on leaf springs per side and the same engine as the Pz.Sfl.IVa. However, the mass dropped to 18 tons, which improved mobility.
Two experimental prototypes of the SPG, which was called leFH 18 (Sfl.) starting with August 13th, 1941, were ready by early January of 1942. The result was a good vehicle that was suitable for supporting tanks. However, doubts about the mass production of the SPG began to appear in the spring. The gun caliber was rather small for such a large and expensive chassis, and the fighting compartment was not very roomy. The engine was proprietary, and it could not use parts from more numerous vehicles, like the road wheels and other components.
It's not surprising that OKH (Oberkommando des Heeres, Supreme Command of the Land Forces) decided to create a medium "self propelled mount" with a more impressive gun. The 15 cm sFH 15 was chosen as the weapon. The gun itself was good, but its mass of 5 tons seriously limited its mobility on the battlefield.
As you can see, the 15 cm sFH 18 was hardly a feather. Imagine being a part of its crew and having to push it across a field...
Rheinmetall-Borsig was chosen as the developer of the new SPG. Krupp's main competitor in the B.W. project, the arms giant quickly found an alternative to the tender that it lost. The conglomerate opened the Alkett factory (Altmärkische Kettenfabrik) in 1938 in Spandau, a suburb of Berlin. Its main purpose was assembly of tanks and SPGs, and that is where the new SPG was developed.
The first vehicles built here were 32 PzII Ausf B tanks, and later the factory build medium PzIII tanks. Starting in 1940, the main product of the factory was the StuG III. Alkett was the only supplier of this vehicle starting with the StuG III Ausf. B and to the Ausf. F/8. Even the StuG 40 Ausf. G, the most numerous type of armoured vehicle in Germany, was largely built in Spandau. It's no surprise that the OKH chose this factory.
The first Geschützwagen für sFH 18/1, late 1942. The large muzzle brake makes this vehicle easy to identify.
Since production of the PzIII and tanks on its chassis was the priority for Alkett, it was quite reasonable for them to choose this tank as the chassis. In real life, things were not so simple. An idea of further development of the PzIII arose in December of 1941. The installation of the PzIV turret and a 75 mm KwK 40 L/43 gun was planned. The tank would be called PzIII Ausf. K. The project did not make it into metal. It turned out that the running gear would have to be redone to install a turret that could fit more powerful armament. That was the beginning of the end for the PzIII.
As for the PzIV, its upper limit was higher at 25 tons. Even though the PzIII chassis was not out of production, as it was used to build the StuG 40 with the more powerful 7.5 cm StuK 40 cannon, Alkett understood that there is no reasonable alternative to the PzIV.
The resulting design was a hybrid using components from the PzIII and PzIV. The running gear of the Geschützwagen III was the same as on the PzIV. The tank also inherited the Maybach HL 120 TRM engine and its cooling system. The hull "tub" was similar as well. The ZF SSG 77 was taken from the PzIII.
A lack of driver observation hatch was also another unique feature of the experimental Geschützwagen für sFH 18/1.
Since the vehicle would house the large and heavy 149 mm howitzer, there was a lot of work that had to be gone on the layout of the vehicle. The result was a combination of various compromises. The engineers had no other choice but to hide the engine underneath the gun. One can only feel sorry for the repair crews that had to deal with these vehicles. In order to remove the engine, the gun had to be removed first, and then the vehicle had to be partially disassembled.
Servicing the transmission was easier, but still could not be done without a crane. A large plate, which included the driver's cabin, had to be removed. As an aside, the radio operator shared the driver's compartment, but had no observation devices of his own.
Layout of the Geschützwagen III/IV.
Alkett had a good reason for making this decision. This rearrangement of its internals gave the Geschützwagen III a roomy fighting compartment that fit not only the howitzer, but also four crewmen. However, it could only fit 18 rounds of ammunition to go with them.
A well designed cooling system left out the "ears" of the Pz.Sfl.IVa. The mass was also 22 tons, same as the Dicker Max, but with a more powerful engine. The Alkett design also had more components in common with tanks that were already in production than Krupp's vehicles.
SPG from the Steel Mill
The first experimental prototype, called Geschützwagen für sFH 18/1, was built by Alkett towards the end of 1942. The experimental prototype used as many components from the PzIV as possible. One of its distinguishing features was a massive muzzle brake. It was quickly discovered that the muzzle brake was unnecessary, as the stability of the Geschützwagen III/IV was stable enough without it. The muzzle brake also kicked up a large cloud of dust when the gun fired.
Assembly line at Deutsche Eisenwerke AG, Werk Stahlindustie, Duisburg.
As a result of trials, the vehicle was improved. The howitzer lost its muzzle brake, and some changes were made to the running gear. The drive sprocket and final drives were taken from the PzIII instead of the PzIV. Considering that the main product at Alkett was the StuG, this was a logical decision, especially since the gearbox was already taken from the PzIII. The vehicle also "grew" auxiliary elements, such as hooks for the tarp. The driver's cabin received an observation hatch, which improved his visibility on the march.
This photo shows that the engine and its cooling system are located underneath the gun.
The issue of the small ammunition capacity was also solved around this time. Alkett did not reinvent the wheel and designed a munition carrier on the Geschützwagen für sFH 18/1 chassis. The vehicle was called Geschützwagen III für Munition and had the index Sd.Kfz.165, same as the Geschützwagen III.
In practice, this was the same vehicle, but without a howitzer and with a shield where its port used to be. The fighting compartment had racks for ammunition. A series of simple operations could convert the vehicle into a Geschützwagen für sFH 18/1. Thanks to this feature, the number of vehicles produced changes depending on the source. The question of how many munitions carriers were later turned into SPGs remains unanswered.
Geschutzwagen III, spring 1943 production.
Meanwhile, Alkett had better things to do than work on a new SPG by late 1942. The monthly production of the StuG 40 grew up to 100 vehicles in November, and 129 in December, even though production of the StuG 40 Ausf. G began that month. The importance of these vehicles can be seen from the fact that they were also produced at MIAG starting in February of 1943. Alkett was also tasked with production of the StuH 42 with a 105 mm howitzer in March of 1943.
It's not surprising that another contractor was found for production of the Geschützwagen für sFH 18/1. This was the Deutsche Eisenwerke AG, Werk Stahlindustie steel mill in Duisburg. The distance between Duisburg and Hessen was about the same as to Dusseldorf. This was symbolic, as the production of Deutsche Eisenwerke AG united Krupp and Rheinmetall's work.
Deutsche Edelstahlwerke AG (DEW) was the supplier of armoured plates for the new SPG. Starting in March of 1943, production of armour was moved to Deutsche Röhrenwerke AG Werk Thyssen.
Geschützwagen III für Munition built on the same chassis.
The first five SPGs were built in February of 1943. At that point, they were called Geschützwagen III. In March, the volume of production reached 26 units, and 49 in April. Starting in May, the Geschützwagen III fur Munition entered production, which decreased the number of SPGs built. In total, 368 SPGs and 96 munitions carriers were built in 1943.
Captured Geschützwagen III at the NIIBT proving grounds.
The complex story of the name of this SPG deserves a special mention. By July 1st, 1943, its name changed to schwere Feldhaubitze 18/1 (Sf) auf Geschützwagen IV, or "heavy 18/1 howitzer on the IV gun vehicle". This title lasted for a month. In early August, the SPG was renamed to G.W.III/IV Hummel für s.FH 18/1 (Sd.Kfz.165). This was the first time the name Hummel (bumblebee) appeared in the SPG's title. However, it only stuck around for a few months. In manual D-653/42, published on October 15th, 1943, the vehicle was named schwere Feldhaubitze 18/1 (Sf) auf GW IV. Even that name did not last long: the SPG was called Geschützwagen III/IV (Sd.Kfz.165) as of November 1st. The name Hummel was no longer used officially, but it remained in practice. In total, the SPG was renamed eight times. The last renaming happened in October of 1944: it became s.Pz.Haub.18/1 auf Fgst.Pz.Kpfw.III/IV (sf) (sd.Kfz.165).
With such a "simple" name, is it any wonder that the military kept calling it "Hummel"? It's worth a mention that the name "Hummel" appeared in Guderian's reports before it was given to the SPG officially, on May 3rd, 1943. It was also used later. The SPG is called Hummel in a report dated May 3rd, 1944. This information name kept on being used at the highest levels as the most convenient.
The mounts for spare wheels and track links are some of the many field modifications.
The SPG changed more than its index. The first serious change in the design happened in the summer of 1943. The location of the muffler in the rear was not the best place for it, and the muffler was removed. The exhaust pipes were shortened and turned sideways so that the gases did not enter the fighting compartment. The space that freed up was used to carry spare road wheels.
Work on bigger changes began in December of 1943. Alkett finally figured out that the radio operator is bored without observation devices. As a result, a new cabin was designed, this time with a place for the radio operator. Like the driver, he received a hatch with an observation port. Another observation port was added to the right. The driver's visibility dropped somewhat, but since it was already far from ideal, this was not a big issue. The new cabin entered production in February of 1944.
The running gear was also changed somewhat in the spring of 1944. The PzIV Ausf. J went into production with a different idler design, and that design migrated to the SPG. The last changes made to the design were to the air intakes in the sides. Combat experience showed that the intakes were vulnerable, so they were moved up. This improvement was implemented in August of 1944.
The muffler means that the vehicle was built before August of 1943.
289 SPGs and 61 munitions carriers were built in 1944. 48 more were built in 1945. The last s.Pz.Haub.18/1 auf Fgst.Pz.Kpfw.III/IV (sf) (sd.Kfz.165) left the factory in March. The total production run was 705 SPGs and 157 munitions carriers. The vehicles received serial numbers 320001-32813. 50 of the munitions carriers were built at Werk Teplitz-Schönau in Teplice. These vehicles had serial numbers 325001–325050. Production here began in early 1944, but the factory was quickly converted to produce Hornisse (Nashorn) tank destroyers, since it used the same Geschützwagen III/IV chassis.
Long Arm of the Wehrmacht's Tank Divisions
Heavy SPG batteries began forming in May of 1943, which were included in self propelled squadrons. According to TO&E K.St.N.461b issued on January 15th, 1943, the third battery of such a squadron included six Geschützwagen III/IV. The table also included two munitions carriers. Tank divisions also received SPGs. Batteries in SS tank divisions also got them. These vehicles were also sent to the 845th and 536th independent heavy artillery squadrons.
The new driver's cabin was put into production in February of 1944.
Since a battery only had 6 vehicles and 2 munitions carriers, units filled up quickly. During the entire production run, Hummels were sent to 40 different units, and impressive number. It's not surprising that the use of these tanks in combat, starting with July of 1943 during the Battle of Kursk, was widespread, and the SPG ended up as one of the symbols of German tank building. At the start of Operation Citadel, the schwere Feldhaubitze 18/1 (Sf) auf Geschützwagen IV could be found in ten different units.
A captured late production Hummel. Officially, the 366th SAP had two of these SPGs, but vehicles with tactical numbers 41, 52, and 53 are known.
Reviews from the front were contradictory. On one hand, the concept of an artillery squadron with a battery of six Wespe and a battery of six Hummels was correct. The combination of 105 and 149 mm guns was suitable for many objectives during a division's attack or defense. The mechanization of artillery noticeably sped up the time required to bring the gun into position and increased the mobility of artillery.
On the other hand, there were many complaints regarding the mobility. There was an issue with poorly trained drivers, but the SPG itself gathered many complaints. Most of them were about the running gear. The main clutch and idlers often broke. Even though the vehicle's mass was only 22 tons, the suspension was overloaded. There were also many teething troubles, which were highlighted by a lack of spare parts.
The loading process. The right rack contained propellant, and the shells lined the floor of the fighting compartment. As you can see, the fighting compartment had no lack of space.
The foreign equivalent of the Hummel was, at the very least, no better. The American Gun Motor Carriage M12 had no fighting compartment at all and the crew had to stand behind it while firing. The American vehicle was also slower and heavier, and carried only 10 rounds of ammunition. Compared to the GMC M12, Alkett's design was a leader in crew comfort.
Complaints about the Hummel kept coming. The issues with the main clutch didn't go anywhere, and many units complained about the engine being too weak. The same complaints were made about the Wespe. One must remember than an SPG is not a tank, but the tankers often forgot that. Issues with spare parts also never disappeared, which often resulted in vehicles lost for technical reasons. Despite all these complaints, the self propelled gun mount concept itself was proven correct.
There were, however, cases in Italy when the artillerymen demanded their towed guns back. This was due to the difficult terrain, which the Hummel was not suited to. For example, after three weeks of fighting, the battery of the 26th Tank Division had one Hummel left out of six.
The most noticeable conversions were done in the 9th SS Tank Division Hohenstaufen. Notice the anti-grenade net above the fighting compartment.
Often, the cause of the loss of SPGs was that they were used incorrectly. Frontline conversions hint at this phenomenon. For example, 9th SS Tank Division Hohenstaufen altered all of their Hummels in a very noticeable way. A special net was installed above the fighting compartment to prevent grenades from being tossed in. Considering that the official task of the self propelled gun mount was firing indirectly, and not fighting the enemy close up, these conversions raise some questions. Complaints about damage to the recoil mechanisms from bullets and shrapnel also indicate that the Hummels were firing directly at the enemy.
Naturally, the vehicle was not meant for this task. Its large size made a good target, and the thin armour left no chance of survival for the crew. The ammunition that lines the sides was also a problem; the Hummel's detonating ammunition rack made for stunning fireworks.
The only known photo of the Hummel-Wespe to date.
The last version of the SPG is known as the Hummel-Wespe. It appeared due to the cancellation of the Wespe in June of 1944. Discussion of creating the Hummel-Wespe began in October of 1944. The vehicle was initially called le.Pz.Haub, light howitzer on a tank platform, and was a GW III/IV chassis with a leFH 18/40 howitzer installed. The front of the casemate was changed to accommodate this, and armour for the howitzer was developed. A net was added to the roof to protect the SPG from grenades.
According to plans, 40 of these SPGs would be built in February of 1945, 50 in March, 80 in April, and 250 in total until the end of June. The reality was different: one experimental Hummel-Wespe was built at Alkett in December of 1944. There is also information about nine more vehicles built in January of 1945. The Hummel-Wespe was supposed to be built at Teplice, since Duisburg was heavily bombed.
A Hummel destroyed during street fighting. Berlin, May of 1945
The Hummel was used until the end of the war. German troops used them during street fighting in Berlin. The Germans weren't the only ones using them in battle. The 366th SAP in the 4th Guards Army had two vehicles officially, and that was not the complete list of such trophies. The service life of the SPG did not end with the end of the war. One SPG was given to Romania, and the French sold five Hummels to Syria in the late 1950s. These vehicles were used in the Arab-Israeli War of 1967.
Despite some drawbacks, the Hummel concept was a correct one. Thanks to these vehicles, tank divisions received much more maneuverable artillery units. After the war, many countries, including the USSR, adopted the concept of high caliber SPGs as a method of reinforcing tank units. The idea of a medium "self propelled gun mount" was also correct. It was developed further into the Waffentrager: an SPG that was as cheap as possible while increasing the mobility of towed artillery.