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Three Inch Halftrack

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Germany produced a large number of well thought out and elegantly composed improvised vehicles during the Second World War. The main character of this article is not one of them. Its large and clumsy appearance war far from perfection. Nevertheless, the 7.62 cm F.K.(r) auf gp. Selbstfahrlafette (Sd.Kfz. 6/3) left its mark on history.

One of the main challenges faced by the Wehrmacht during Operation Barbarossa was the sudden encounter with T-34 and KV-1 tanks. Their armour turned out to be difficult to handle for the 37 mm Pak anti-tank gun. Even the 50 mm Pak 38 was not available in sufficient numbers, and the 75 mm Pak 40 only entered production in January of 1942. Using captured field guns as a temporary solution seemed sensible. In part, the Germans converted over 3700 French Mle.1897 75 mm guns into improvised anti-tank weapons. The Germans also captured about 1250 Soviet 76.2 mm model 1936 divisional guns (F-22) and a few hundred modernized model 1939 guns (F-22USV) from mid-1941 to mid-1942. 

Conversion into an anti-tank gun involved drilling out the breech to accept new rounds developed by German specialists using the 716 mm long casing from the Pak 40 gun. The converted F-22 was indexed Pak 36(r) and the converted F-22USV became the Pak 39(r). Production began in 1942 and deliveries lasted all the way until January of 1944. Overall, the Wehrmacht received 560 guns on towed carriages with as many as 300 Pak 39(r) among them. 894 guns (all Pak 36(r) ) were built for self propelled guns.

Temporary solution

Most Pak 36(r) guns went to arm Marder tank destroyers built on the chassis of light tanks. Attempts to create a tank destroyer with the foreign gun on a halftrack chassis actually predate them. Alkett was given directions to begin working on this topic on August 14th, 1941. Development was targeted at the German Africa Corps. Initial production plans were limited to 20 SPGs.

Sd.Kfz.6 halftrack (BN 9 variant) used as the chassis.

The 5 ton Sd.Kfz.6 hafltrack created by Büssing-NAG back in 1934 was chosen as the chassis. This vehicle went through several modernizations by the start of WW2. Its most modern variant at the time was called BN 9. This variant featured a 115 hp Maybach HL 54 TUKRM engine (previous versions used 100 hp engines) and a 13-seat hull. In addition Büssing-NAG, these halftracks were built at BMM in Prague. The basic BN 9 variant was supplemented by the BN 9a with an improved braking system and the BN 11 with a 130 hp engine. 687 vehicles of this type were built before 1943.

The 5-ton tractor was the least desirable of all German halftracks. Initially it was meant to tow the 105 mm leFH 18 howitzer, but the lighter Sd.Kfz.11 could handle this job at two thirds of the price. Engineering units preferred the more powerful 8-ton Sd.Kfz.7. It's not surprising that the Germans tried to fit the Sd.Kfz.6 somewhere else, including as an SPG chassis. The most common type was the Sd.Kfz.6/2 SPAAG with a 37 mm gun (332 units produced in 1942-43). The tank destroyer was much less common.

The prototype of the tank destroyer was ready in late August or early September of 1941. The speed of production was aided by the simple (downright primitive) design. Only the fighting compartment was armoured, the engine and driver had no protection at all. Gunnery trials took place at the Kummersdorf proving grounds on September 10th. 44 shots were fired. The vehicle passed trials without any comments, but the prototype was still modified. The radiator shield was removed. It was initially installed to protect the radiator from the blast of the gun, but trials showed that it was safe anyway. A large opening was made in the rear of the casemate to make replacing the gun easier. Due to the rush, the prototype had only a mild steel door to cover the opening.

Sd.Kfz.6/3 tank destroyer.

A second stage of gunnery trials took place on September 17th. Mobility trials followed. As a result, Alkett received an order for nine SPGs delivered in October-November of 1941. This new SPG was named 7.62 cm F.K.(r) auf gp. Selbstfahrlafette (Sd.Kfz. 6/3) or 7.62 cm field gun (Russian) on an armoured self propelled mount. Some publications assign it the nickname Diana, but this is a mitsake. Thomas Jentz and Hilary Doyle consider this to be the name of a later vehicle on the Sd.Kfz.6 chassis with the Pak 36(r) gun tested in 1942. Tom Cockle considers the name Diana to be a British invention altogether.

Design

The Sd.Kfz.6/3 SPG was based on the BN 9 variant of the Sd.Kfz.6. In addition to the aforementioned new engine, it had a torsion bar suspension instead of leaf springs and seven road wheels instead of six. The 115 hp engine gave the 10-10.5 ton vehicle a top speed of 50 kph. The fuel tanks held 190 L of fuel, which gave it a range of 220 km on a highway or 110 km off-road.

The Sd.Kfz.6/3 had a large cutout in the front of the casemate.

A 3.6 m long, 2 m wide, and 1.5 m rectangular casemate was installed on top of the truck bed. The casemate had a large cutout in the front where protection was only offered by the 3 mm thick gun shield. The casemate was open from the top. Three pipe braces allowed the crew to install a tarp to protect from precipitation. Two doors 0.9 m wide and 1 m tall were cut into the sides of the casemate. A 0.6 m wide door was cut in the back. The casemate armour was 4.5 mm thick. Some older sources give a thickness of 8-10 mm, but this is not corroborated by German reports which state that the armour of the SPG "[...]does not protect from small arms fire". As mentioned above, the engine and cab were not armoured at all. Theoretically, the thin armour of lighter vehicles was supposed to be compensated by agility and ability to hide, but the height of 3 meters at a length of over 6.3 meters and width of almost 2.7 meters made this tank destroyer a very easy target.

Sd.Kfz.6/3 with an open side door.

The SPG was armed with the 76 mm FK 296(r), a captured F-22 not converted to an anti-tank gun (these conversions only began in 1942). Even using the stock Soviet casings that were shorter than those used in the Pak 36(r), the gun penetrated 67-77 mm of armour at 1000 m (depending on the type of shell). Since the project was urgent, Alkett's engineers didn't spend too much time thinking about the mount and installed the entire gun on the halftrack, wheels included. The trails had to be trimmed a bit. The mount was bolted to the floor of the fighting compartment. Traverse was limited to a 60 degree arc (30 left and 30 right) with elevation from -7 to +20 degrees. Different sources give the ammunition capacity as 20, 64, or even 100 fixed rounds of ammunition. 40 more shots were carried in the Sd.Anh.32 single axle trailer.

Destroyed Sd.Kfz.6/3 halftrack. The stock gun carriage can be seen.

The crew of the SPG consisted of six crewmen: driver, commander, gunner, loader, and two ammunition carriers. The commander had an SMG as an auxiliary weapon, the rest of the crew had only pistols. A platoon of these tank destroyers defined in K.St.N. 1149 approved on November 13th 1941 authorized three SPGs with crews as well as a platoon HQ (six men, a light car, and a motorcycle). 

Service and combat

All nine Sd.Kfz.6/3 arrived at the tank school in Wünsdorf in the second half of October 1941. On November 1st they were formed into a company. The crews broke in their vehicles and tested them at the proving grounds. The tank destroyer company arrived in Italy in late December 1941. The first six Sd.Kfz.6/3 arrived in Tripoli on January 5th 1942, the remaining three joined them on February 23rd.

Sd.Kfz.6/3 and a Panzerjager I of the 605th Tank Destroyer Battalion.

The Sd.Kfz.6/3 unit made up the 3rd company of the 605th Tank Destroyer Battalion of the 90th Light Division. Two SPGs were lost for unknown reasons in April of 1942. All seven remaining ones took part in Operation Venezia (the attack of German-Italian forces on the southernmost part of the Gazala Line) on May 26th. Two more SPGs were lost in these battles. One was sent to repairs, leaving only four Sd.Kfz.6/3 in service. Two took part in the taking of Tobruk on June 20th 1942.

Sd.Kfz.6/3 prepared to fire.

Two more Sd.Kfz.6/3 were destroyed by enemy fire by July 1st 1942, leaving just three SPGs with the 605th battalion (one in serviceable condition). The last attempt to punch through the British defenses at El Alamein cost the Germans one more Sd.Kfz.6/3 destroyed on August 31st. The remaining two SPGs were back in action by the start of the British offensive on October 23rd, but were both lost by December 2nd.

Captured Sd.Kfz.6/3.

The results of the use of the Sd.Kfz.6/3 in combat were summarised in a report by a signals officer in the ordnance section at the HQ of Tank Army Africa. It noted that the FK 296(r) can confidently defeat any enemy tank. However, the stock sight of the F-22 used in the SPGs was ill-suited for direct fire on small targets. The size of the SPG ("as big as a barn door") thin armour, and low off-road speed made it very vulnerable. This ersatz was not very successful and was not developed any further.


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