Monday 19 July 2021

Overgrown Cricket

 The Germans focused a lot of effort on mechanization of artillery. They were the first to use SPGs of all types in large numbers. The most common German fully tracked armoured vehicle was an SPG. Light and medium SPGs were common, but heavy ones not so much. Only the Jagdpanther heavy tank destroyer was built in large numbers, but only 90 Ferdinands and 85 Jagdtigers. Compared to the ISU-152 and ISU-122 these are negligible numbers. Heavy "weapons carriers" were in the worst position. Not a single one was mass produced and only one prototype was built. This was the Geschützwagen Tiger für 17cm K72 (Sf) or Grille 17/21.

A bigger weapons carrier

Good experience in development of medium SPGs spurred on further work. There was experience in development of a heavy SPG by early 1942, the Pz.Sfl.V bunker buster on the VK 30.01(H) chassis. Even though only two vehicles were built, one may consider this program a success. The vehicle may have been slow and the pressure on the suspension was high, which led to rapid wear of the road wheels, and ammunition capacity may have been low, but the very act of motorizing such a large and heavy weapon as the 12,8 cm Flak 40 L/61 was already an achievement.

Like the 17 cm Kanone 18, the 21 cm Mörser 18 was used in a direct fire role. In this photo you can see the traversing base. The same solution would be used in the SPG with this weapon.

There were other weapons that also required self propelled gun mounts, primarily the 149 mm sFH 18. The story of the Hummel SPG is well known, but it was far from the only one. A program for self propelled gun mounts under the name Grille was launched in 1942. It had little to do with the SPG on the Pz.Kpfw.38(t) chassis. According to surviving documents, the series included the Grille 10 (105 mm L/35 howitzer), Grille 12 (128 mm L/50 gun) and Grille 15 (149 mm L/35 gun-howitzer). The names Grille 12 and Grille 15 covered a whole series of vastly different projects. The VK 30.02 (M) and later the Panther was selected as the chassis.

Finally, another project was described on May 6th, 1942: the 17 Kanone L/50 in Sfl. No chassis was specified, just the mass: 37 tons. The high speed was expected to be quite high, 40-50 kph. According to requirements, the vehicle needed 360 degree traverse with a rate of fire of 2 RPM. While the chassis was still unknown, at least a mass produced gun was selected, the 17 cm Kanone 18. This quite heavy (17.5 tons in combat position) 173 mm gun was built in some numbers (338 units). Deploying this weapon to fire was a lengthy task.

A model of the 17 cm K Sfl., early July, 1942. This model was shown to Hitler.

The cannon shared a carriage with the 211 mm 21 cm Morser 18 howitzer, so its full name was 17 cm Kanone 18 in Mörserlafette. One feature of this carriage was that it had a large central foundation, which allowed it to rotate 360 degrees. The fact that the two guns shared a carriage was recognized, and as of May 6th the project was called Selbstfahrlafette mit 17 cm K bzw. 21 cm Mörser. The requiement to turn the gun in the same way as the towed version was specified. The vehicle would drive up on a foundation and then be able to turn a full 360 degrees. This was a bold and quite complex idea, but orders are orders. The vehicle was developed at Krupp. Development was led personally by Erich Muller, Krupp's chief designer. There is nothing odd about this choice, as Krupp was a cannon company, and the Grille program was generally their domain anyway.

Process of deploying the gun. This design has many differences from the final Grille 17/21.

A model of the 17 cm K Sfl. was finished by July 3rd, 1942, and was demonstrated to Hitler shortly after. Some state that this vehicle was based on the VK 45.02 (H) chassis, but it was still in early stages of design. However, Krupp closely cooperated with the 6th Department of the Ordnance Directorate, where they got their orders for chassis design. Kniepkamp was personally overseeing the project, and so the 17 cm K Sfl. received some components sooner tahn the VK 45.02 (H). For instance, the engine was upgraded to the prospective 750 hp Maybach HL 230 (the original requirement was for the 650 hp Maybach HL 210), Henschel KL 800/320 track links, and a 7-speed ZF-Alklauen AK 7-200 mechancial gearbox in July of 1942. All of these components only appear in correspondence pertaining to the VK 45.02 (H) in August of 1942. Kniepkamp expected the top speed to be 60 kph, at least the chassis ought to allow for this speed.

The SPG in battle position. This photo doesn't show the foundation underneath the floor plate. The design called for 360 traverse to be achievable without the use of the vehicle's running gear.

A meeting was held on August 14th, 1942, attended by Muller, Kniepkamp, Wolvert, and others. The decision to make the full scale model of the 17 cm K Sfl. was made at this meeting. This model would already have some differences from the scale model. Another change was made in September of 1942. The name Grille 21 was first used. The name Gerät 5-1702 was also used by the OKH. A month later the vehicle's most recognizeable name finally appeared: Grille 17/21.

Design in treacherous conditions

The Grille 17/21 took shape in early 1943. The VK 45.02 (H) influenced the work, as the chassis changed several times. The requirement for parts commonality forced Krupp to trail VK 45.02 (H) development. In any case, blueprint AFK 70215 dated January 22nd, 1943, already gave the overall impression of how this vehicle was going to turn out. The Grille 17/21 did not change significantly after that. The chassis was considerably heavier than expected. After all the changes, the mass went from 37 tons to an impressive 55 tons. The top speed dropped to 48 kph, still very high for such a heavy vehicle.

The full scale model of the Grille 17/21. The vehicle weighed 55 tons by this point and would only get heavier.

The overall concept of the Grille 17/21 was unchanged. The Grille program required the use of ordinary towed guns with minimal changes. For instance, the Grille 17/21's weapons would receive a perforated style muzzle brake, which was necessary to reduce the recoil. The guns were identical to their towed variants otherwise. As the Grille concept required, the gun could be extracted from the vehicle and turn into a towed gun merely by adding wheels.

A full size mockup of the fighting compartment of one of the Grille 17/21 iterations.

The concept seemed like a failure from the start, as the Germans caused themselves problems. It's easy to understand the idea of a convertible towed/self propelled gun, but the question is why? This "solution" made the fighting compartment significantly more complicated and made the vehicle heavier. In addition to the oscillating part of the gun, the vehicle had to truck around the carriage that was not light or small. The Germans were unwilling to let go of the idea of turning a self propelled gun into a towed one. Recall the 15 cm sIG 33 B Sfl which preserved the carriage, albeit without wheels. Germany only dropped the idea of 1944 when the decision to only install the oscillating part of the gun on weapons carriers was mdae. The requirement to be able to transplant them onto towed carriages remained.

Stand-ins for the crew.

Compared to the 17 cm K Sfl. shown to Hitler in July of 1942 the final variant of the Grille 17/21 changed significantly. Initially it was supposed to have the same chassis as the VK 45.02 (H), but it quickly turned out that the hull had to be much longer to fit the gun and other components properly. Only the overall layout and the concept of the fighting compartment with the gun keeping its original carriage remained. The hull length grew to 9500 mm (to compare, the Tiger Ausf.B's hull was 7134 mm long), which contributed to the increase in mass. The fighting compartment took up about 2/3rds of that length. This was the price for fitting the gun with its carriage. The VK 45.02/Tiger Ausf.B donated only the running gear and the overall design of the front plates. The thickness of the armour was much less than that of the original tank, same as on any other weapons carrier. The front of the hull was only 30 mm thick, the rest of the plates were 16 mm thick. Since the vehicle's height came up to 3150 mm it had precious few chances of survival if the enemy got close. One extra pair of road wheels was added to the front and the back to compensate for the length of the hull. Panther II tracks were going to be used as transport tracks.

The result of insisting on the original carriage. The inside of the vehicle was cramped, to say the least.

The Grille 17/21 was crewed by 8 men, two of which were in the driver's compartment. There was no link to the fighting compartment, as the engine was right behind them. As of the end of January 1943 the Grille 17/21 still used the ZF-Alklauen AK 7-200 gearbox (although the internals of the SPG continued to lag behind those of the tank). The Tiger III appeared in February of 1943. This tank shared components with the Panther II. As a result of all the changes the tank received a new gearbox, the Maybach OLVAR OG 40 12 16B, although this gearbox was originally intended for the Tiger II and later migrated to the Tiger Ausf.B. This flux affected the rest of the vehicle's components. The ZF-Alklauen AK 7-200 gearbox remained attached to the Grille 17/21 project until the end of August, when the Maybach OLVAR OG 40 12 16B was finally enstated as the SPG's gearbox.

A partially complete 17 K.72 (Sf) GW.Tiger at the Henschel proving grounds in Haustenbeck.

It is often said that Hitler ordered that development of the chassis should be paused in order to work on tank production in April of 1943. In theory this was so, in practice not so much. Krupp, Henschel, OKH, and the 4th and 6th Departments of the Ordnance Directorae continued to correspond on the Grille 17/21 even after April of 1943. Either Hitler's orders didn't worry the participants, or historians missed something. In the fall of 1943 the vehicle was often called Grille 17/21 mit einbauteilen Tiger II, suggesting parts commonality with the Tiger Ausf.B. Letters mentioned the due dates for various components and assemblies, which kept slipping. As of September delivery of the components for the new prototype was expected by January of 1944. This was not because of the Fuhrer's prohibitions, but because of constant changes to the design and renegotiations.

The SPG was so enormous that it had to be photographed in parts.

Work on the vehicle really died down in early 1944, but it was revived in July. The reworked Grille 17 was ready by August 4th. The mass grew to 60 tons, the top speed decreased to 45 kph. The overall layout of the chassis was nearly the same, but the driver's compartment was presented in greater detail. The driver received an observation device similar to the one developed for the Typ 180 in the fall of 1942 and later transferred to the VK 45.03. The radio operator received a machine gun in a ball mount. More changes were made to the fighting compartment. The mufflers were removed and the exhaust pipes led straight out. The final variant of the Grille 17/21 had a travel clamp for the gun. One of the requirements for the design was the ability to fit into the 60 ton railway platform used for transporting the Tiger Ausf.E. The Grille 17/21 was narrow enough (assuming the transport tracks were used) but it was too tall. The solution to this problem was quite original. The sides of the casemate could fold in, and the upper part of the front could also fold.

American soldiers for scale inside the fighting compartment of the 17 K.72 (Sf) GW.Tiger.

Work on the model continued in parallel. Krupp built a wooden model of the fighting compartment where they laid out the locations of the crew and ammunition. The latter was a big problem: only 5 rounds were carried for the 17 cm Kanone 18, and only 3 for the 21 cm Mrs 18. The vehicle could only be used in conjunction with munitions carriers.

The same SPG outdoors.

Project documentation was finished sometime by mid-September 1944. Orders to build a prototype followed. The 173 mm Kanone 72 (effectively the Kanone 18 with a muzzle brake) was used as the armament. The vehicle was therefore referred to as the 17 K.72 (Sf) GW.Tiger. The designation Geschützwagen Tiger für 17cm K72 (Sf) can also be found. The orders to build a prototype were clearly too late. Half a year prior the odds of completion were high, but by late 1944 Krupp's factories were bombed regularly. Only one chassis was partially completed and sent to the Henschel proving grounds in Haustenbeck (near Paderborn). Attempts were undertaken to complete the vehicle, but work proceeded slowly. The last information regarding the 17 K.72 (Sf) GW.Tiger was dated February 1945. The vehicle was still awaiting tracks and other components, wihch never arrived.

A very large trophy

The Henschel proving grounds were captured by the Allies in early May of 1945. Representatives of British and American military intelligence arrived on the scene immediately. Joint inspection of the materiel at the proving grounds commenced. The Allies were very lucky, as they got their hands on most prototypes of tanks and SPGs developed by this company. For instance, the E-100 superheavy tank prototype was found here. 

The Geschützwagen Tiger für 17cm K72 (Sf) looked like this when it was captured in early May of 1945.

In addition to the 17 K.72 (Sf) GW.Tiger (called Grille in correspondence), the Kanone 72 gun was found at the proving grounds. Some researchers confuse it for the E-100's gun, but that gun was not supposed to have a muzzle brake. No technical documentation was found, which explains the odd descriptions that were recorded.

The 17 cm Kanone 72 had a muzzle brake, unlike the regular towed gun. Certain "experts" decided that this was the E-100's gun.

It seemed that the American and British impressions of the German heavy SPG were poor. Even though the 17 K.72 (Sf) GW.Tiger was much more complete than the E-100, only a few paragraphs on it made their way into each of the two reports composed in May of 1945. One of them is very misleading, as it estimates the vehicle's mass at 120 tons, twice as high as it really was.  

The 17 K.72 (Sf) GW.Tiger on its way to the UK. It was scrapped there, a move which they now no doubt regret.

The vehicle's further fate was a sad one. The 17 K.72 (Sf) GW.Tiger was never fully assembled, even though this was possble. The SPG was loaded on a trailer designed for super-heavy cargo and transported to the UK. The top of the casemate was detached and dumped inside the fighting compartment so the vehicle was easier to transport. Like other vehicles captured in Haustnbeck, the 17 K.72 (Sf) GW.Tiger was scrapped. Only the Jagdtiger and second Tiger Ausf.B prototypes survived. This is considered a tragedy today, but neither the Americans nor the British were concerned with "excess" armoured vehicles at the time.

30.5 cm schwerer Granatenwerfer in Selbstfahrlafette, early 1945.

In conclusion, let us mention a few projects directly connected with the Grille 17/21. These vehicles were designed in cooperation with Škoda. A number of weapons were designed in Pilsen under the supervision of the SS. These included the superheavy 305 mm mortar (30.5 cm Granatwerfer). Development began in January of 1945 and finished 20 days later. A prototype was even built in April of 1945. It could fire a 160 kg mine to a distance of 10 km. What is more interesting is that a self propelled variant named 30.5 cm schwerer Granatenwerfer in Selbstfahrlafette was developed at the same time. The Tiger Ausf.B chassis lengthened by two road wheels was used for this vehicle. The mass was only 55 tons. A special trail located under the floor was deployed before firing. The mass was lower than that of the Grille 17/21 since only the oscillating part of the mount was located inside the SPG. The ammunition capacity is unknown, but it would have been higher than the Grille 17/21 had.

The 42 cm schwerer Granatenwerfer in Selbstfahrlafette was also designed.

Škoda was working on an even larger weapon, the 42 cm schwerer Granatenwerfer. Work began in February of 1945. This mortar had a similar range, but a much heavier shell: 400 kg. It was never built since the estimated mass of 21.6 tons was too great. Škoda also designed an SPG variant, the  42 cm schwerer Granatenwerfer in Selbstfahrlafette. It was similar to the 305 mm SPG with the same deployable trail. Its dimensions were larger and the weight reached 65 tons. Neither SPG made it past the draft stage, although these projects were quite interesting. These were the largest guns tested on the Tiger Ausf.B chassis. Škoda was not a mere bystander in the Tiger Ausf.B program, but also built hulls for it. It is unknown who initiated this work, perhaps someone in the SS decided to make use of their "in-house" engineers.

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