If you have no road work for your tractor perhaps a crawler would be a good option. Jonathan Whitlam looks at the original tracklayer – the Caterpillar.

Steel tracks instead of wheels can provide many benefits such as increased traction, especially in wet and sticky conditions, plus the added attraction of lower soil compaction thanks to the greater surface area in contact with the ground. For the best part of a century the Caterpillar name has been synonymous with this type of machine.

It was an American called Benjamin Holt who produced the first really successful tracklayer in 1904 which was powered by steam followed by a petrol engined version in 1906. It was also the Holt Tractor Company who actually first registered the Caterpillar name.

It took until 1925 however before the Caterpillar Tractor Company of Illinois was formed when the Holt company merged with former competitor Best Tractor Company, a firm that had also established itself as a tracklayer builder.

Both these companies were early to see the advantages of using endless steel belts instead of wheels and both built truly enormous machines.

After the formation of the Caterpillar Tractor Company crawlers began to be built of a more manageable size which appealed to the average size farmer as well as those with thousands of acres to cover.

One of the most popular of the early Caterpillar crawlers was the Caterpillar Twenty which was a 25hp machine powered by a four cylinder petrol-paraffin engine driving through a three speed gearbox. From 1934 the Caterpillar 22 became the best selling model and this machine was popular here in the UK.

Then in 1931 Caterpillar helped to pioneer the use of diesel engines in farm tractors with the introduction of the four cylinder engined Caterpillar 65 which was started with a 10hp two cylinder petrol ‘donkey’ engine. The 65 was followed by other diesel models including the 41hp Caterpillar 35 and the 82hp Caterpillar 75.

The 1930s was very early for the use of diesel power, especially in the USA, but the Caterpillar machines were very popular and because of the increased traction offered by the steel tracks could make good use of the lower revving diesel power units.

The problem was of course starting these high compression engines; petrol powered machines could be turned over by means of a hand crank but this was not practical with the diesel units and so hence the use of small ‘donkey’ petrol engines to start the bigger diesel unit. In the States these were known as ‘pony’ engines. Caterpillar really hit gold in 1935 when they first introduced what was to be an extremely long running series of crawlers. The D series was made up of five models initially known as the D2, D4, D6, D7 and D8.

The D2 was a four cylinder 30hp crawler, the D4 had 40hp from its four cylinder motor while the D6 had a six cylinder motor pushing out 78 horses, the D7 89hp from a four cylinder engine and the flagship D8 put out a hefty 127hp from its six cylinder diesel engine.

All these tractors made use of a two cylinder ‘donkey’ engine for starting which ranged in power from 10hp on the D2 to 24hp on the mighty D8.

For the full story see August's issue of Smallholder