With the expansion of the British Army in late 1914 and early 1915, there was a severe shortage of tractors suitable for hauling the heavier artillery pieces. At the start of World War 1, steam-driven traction engines had been used by the RGA for towing medium and heavy guns with the exception of a few batteries of mediums which were drawn by teams of Clydesdale draught horses. However, as the war progressed petrol-engined mechanical transport gradually superseded the horse. The reason was that it was soon found out that horses were inadequate in the congested and usually muddy conditions of the Western Front for pulling medium or heavy guns due to the large teams required. The animals remained with the horse and field artillery batteries for the duration, therefore, while tractors were used for larger weapons. Steam traction engines were pressed into service initially but the first "standard" tractor adopted in quantity was the Holt, an American-built agricultural tractor with petrol engine and crawler tracks.
The founding of the Holt Company goes back to 1890, when Benjamin Holt (while working at the Stockton Wheel Co. with his brother, Charles) introduced his first steam traction engine. In 1892, Benjamin split off and formed the Holt Manufacturing Co., concentrating on the manufacture of steam traction engines. Between 1890 and 1904, Holt Manufacturing produced about 130 steam-powered tractors. After successful trials in 1904 and early 1905, Holt moved ahead with plans to offer a track-type tractor. The manufacture of steam engines ended about this time as Holt concentrated on tracked tractors driven by petrol motors.
A few of these tracked tractors had been imported to Europe as early as 1912 for commercial use, and the Holt company had appointed agencies in various countries. Soon after war was declared, the Royal Artillery was casting round for suitable readily available tractors and selected the Holt 75-h.p. model and orders were placed. The fact that this vehicle had tracks, and therefore had a limited off-the-road capability was a lesser consideration than its availability.
In January 1915 the first deliveries were made and after assessment trials at Aldershot the Holts were sent to France where they became a major artillery vehicle for the next four years, mainly engaged in hauling medium guns like the 6 inch howitzer and the 60 pdr., and later the 9.2 inch. To the men these vehicles were popularly known as "Cats". (Cats = Caterpillar Tractors). According to one source, the Holt company photographer coined the term "Caterpillar" in early 1905 after watching Holt’s experimental machine work its way across a field during trials. Holt trademarked the name in 1910.
The Holt 75 h.p. tractor weighed about 15 tons and it had a top speed of just over 3 km/h for towing and 8 km/h unladen. Steering was effected by locking the tracks in the direction of the turn and the braking action was controlled from a steering wheel. There was a jockey wheel at the front to assist stability and this was carried in a forward extension of the chassis.
By later standards the Holt had a poor cross-country ability, but its appearance was one of the factors which led indirectly to the development of the tank. Colonel E. D. Swinton, while serving temporarily in France, heard that the Holt had been adopted by the Royal Artillery and conceived the notion of an armoured version of the vehicle as an "armoured machine-gun carrier" which would carry troops and their guns to storm trenches. At that period, late 1914, the fighting on the Western Front had already degenerated into the trench warfare conditions which led directly to the appearance of tanks as a means to overcome the power of the all-dominant machinegun. In the event, tank development in Britain took another course. Though Holts were tested - and rejected - for possible cross-country use with armoured troop carrying trailers. In the US, the Holt Company used a Holt-type of chassis as a basis for a Tank design, tested but never adapted by the US Army.
However, the Holt tractor remains historically one of the most important military vehicles of all time. One Holt 75-h.p. vehicle was purchased and tested (in Tunisia) by the French Army for possible adoption as an artillery tractor. But France later produced vehicles inspired by the Holt and did not herself use this type in quantity. Two armoured versions of the Holt were produced in America for possible use as tanks (though they were not adopted), and Holt components formed the basis of the only German tank to see service, the A7V and provided the inspiration for the French tanks which appeared in 1916.
In British use, however, the Holts remained in service only as artillery tractors, some lasting well into the twenties. By 1918 they were being used also, to haul 3-inch A.A. guns. In Mesopotamia they were used with tracked trailers to take supplies over the desert in addition to their artillery duties. Holt Tractors were also used by the Austro-Hungarian Army in WW1 (they were built under licence in Budapest).
Main source: C. Ellis & D. Bishop: "Military Transport of World War I".
There is a kit of this vehicle made by B.K. Modelcraft, but I haven’t seen it. Also, in the autumn of 2006, Retrokit plans to issue a kit.