Pat Ware looks at the half-tracked truck and what proved to be a cul-de-sac in the development of improved mobility for soft-skinned vehicles

Although the Great War is generally considered the first conflict in which mechanisation played any significant part, the continuous heavy shelling, combined with the inevitable flooding of the shattered ground, frequently rendered huge areas all but impassable to the wheeled vehicles of the period. However, with their endless track systems, no matter how primitive, the early tanks and heavy artillery tractors were less easily defeated by the same ground conditions. On the downside, their unreliability and the lack of suspension made for a slow and uncomfortable ride. What was needed was some sort of compromise.

In a search for improved mobility, the French Delahaye company had, in 1915, produced a tracked bogie that could be used to replace the rear axle of a conventional wheeled vehicle to produce what came to be known as a ‘half-track’. They were not alone in pursuing this course, and the German Daimler company had also been experimenting with motor trucks on which the rear wheels were replaced by a tracked bogie. Similarly, in the USA, Nash Quad, Mack, Holt and Lombard had also produced primitive half-tracked machines. The well-known tank designer, J Walter Christie, had also flirted with the concept, producing several variations of a tracked bogie that could be used to replace the rear axle(s) of a conventional truck.

However, the first really successful half-tracked vehicle to be developed was almost certainly the Citroen-Kégresse of the early 'twenties. Adolphe Kégresse, a French engineer employed to look after the motorcars of the Russian court, had developed his endless rubber track system to enable the Tsar to drive with equal facility over metalled roads, deep mud and snow during the Russian winter in what was effectively little more than a modified car or light truck.

A key part of the development was almost certainly the inclusion of suspension for the rear bogie. His system demonstrated how the mobility of wheeled vehicles could be improved without necessarily involving the expense, complexity and inherent unreliability of a fully tracked machine. Kégresse was forced to leave Russia after the 1917 Revolution, and brought the system back to his native France, where he managed to convince the entrepreneurial André Citroën that there was merit in developing half-tracked vehicles for use in the French overseas’ territories, where metalled roads were poor or non-existent. A Kégresse bogie was fitted to a Citroën B2 motorcar to produce the Citroën-Kégresse P2. At military-vehicle trials held at Satory in 1923, 1924 and 1925, the P2 was the only vehicle in its class to be awarded a Government subsidy. By 1927, the P2 had been replaced by the P7 with an improved positive drive system, and this led to the P107 of the late ‘thirties.

It is said that Citroën always had his eye on marketing opportunities, and a series of so-called cross-country 'raids' through Africa were used to demonstrate the effectiveness of the concept. Needless to say, it wasn't long before the French Army started to buy Citroën-Kégresse half-tracks.

A company was established to market the Citroen-Kégresse in Britain, and a small number of the half-tracks were employed by the Army as staff cars, the King and Queen being famously photographed in one at Farnborough. However, the Mechanical Warfare Experimental Establishment (MWEE) was far keener to encouraging domestic manufacturers to adopt the system or to develop their own version of it. During the mid to late 'twenties, MWEE organised demonstrations of half-tracked trucks from Albion, Burford, Morris-Commercial, Guy and Crossley, all of which had been fitted with either Kégresse or Roadless tracked bogies; the latter inspired by the Kégresse system and developed by Philip Johnson of Roadless Traction Limited. Sadly, the British Army remained unconvinced that this was the way forward, seeing the half-track as too much of a compromise.

In the USA, there were experiments with a Kégresse-equipped Citroën, and Kégresse tracks were fitted to a Model T Ford, but it is said that Henry Ford remained unimpressed. A year later, in 1932, a number of Ford chassis were also fitted with tracks by James A Cunningham of Rochester, New York. None of these experiments seem to have come to much and it wasn't until the work carried out by GMC, Cunningham and Marmon-Herrington, in conjunction with the US Ordnance Department, that the well known armoured US half-tracks of WW2 started to evolve. With its endless rubber track reinforced by steel cables, the bogie adopted for these machines bore more than a passing resemblance to the Kégresse system.

However, like the British, the US Army remained unconvinced as to the advantages of half-tracked trucks and experiments in this direction never really progressed beyond the trials stage. Germany, on the other hand, was an enthusiastic user of the half-track, with the Wehrmacht seeing considerable benefit in the off-road performance of such machines when compared to the equivalent wheeled vehicle.

A series of sophisticated standardised half-track vehicles was developed in six weight classes from the mid-thirties. The smallest of these was the curious SdKfz 2, the motorcycle-based NSU Kettenkraftrad or Kettenkrad, whilst the largest was the 18-ton SdKfz 9 FAMO; in between came 1-ton (SdKfz 10), 3-ton (SdKfz 11), 5-ton (SdKfz 6), 8-ton (SdKfz 7) and 12-ton (SdKfz 8) machines, all designed to a similar pattern. Eschewing the simplicity of the endless rubber-tracked Kégresse bogie, the sophisticated German half-tracks employed pin-jointed all-steel tracks suspended on torsion bars or semi-elliptical leaf springs.

The vehicles were originally intended for use as prime movers for artillery as well as personnel and cargo carriers, but late in the War, their weight, expense and complexity saw them replaced by the Maultier – a standard military truck on which the rear wheels had been replaced by a far simpler track system. Produced in 2-ton and 4.5-ton weight classes, examples of the Maultier were produced by Ford using the V3000S chassis, by Opel who used their 3.6-4200 Blitz chassis, Klockner-Humboldt-Deutz (KHD), and Mercedes-Benz. It is said that the vehicle was originally based on a field modification that saw the tracked system of a British Bren Carrier fitted to a Ford truck in the Soviet Union. Despite the relative crudeness of the design when compared to the earlier standardised vehicles, the Maultier was surprisingly successful, with some 5000 examples produced.

During WW2, similar experiments were carried out on the Allied side, using Australian Chevrolet, International and Ford chassis using either the track and bogie system of the British Bren Carrier or the US M3/M5 half-track. However, there does not appear to have been any series production.

In Britain, there was a half-tracked version of the 3-ton Bedford QL, again using the track system of the Bren Carrier, and components from a Valentine tank were used by AEC to produce a half-tracked version of the Matador. In 1944, six prototypes were produced by Morris-Commercial Cars and Bedford for a light artillery tractor dubbed the 'Traclat' or BT. The tracked bogie was based on a captured German SdKfz 7 8-ton half-track but, despite impressive performance, it came too late in the War to make any real impact and there was no series production.

There seemed little enthusiasm for half-tracked soft-skins in the USA despite the obvious success of the M3/M5 armoured vehicles, but there were experiments with a half-tracked Jeep using at least two different track systems, and an experimental 2.5 ton half-tracked truck was built by Autocar for possible use in the Soviet Union. Both ZIS and GAZ in the Soviet Union had also produced half-tracked cars and trucks, generally based on a conventional wheeled chassis, but the lack of front-wheel drive and use of low-powered engines restricted their performance.

After 1945, the improvements in all-wheel drive trucks saw the half-tracked vehicle fall from favour. In the late 'seventies, the idea was resurrected by Laird in North Wales, who used the modified track system of the British CVR(T) (combat vehicle, reconnaissance, tracked) for their Centaur half-tracked Land Rover. Despite trials with the British Army and others, the vehicle was never put into series production.