Super-dozer – the Komatsu D455A

Second of the very large track type tractors, or ‘Super-Dozers’ to emerge during the 1970s (the first was the Allis-Chalmers HD-41), the Komatsu D455A went on to carve a very respectable name for itself. By Richard Campbell.

Komatsu Japan has a very long history dating back to 1894 when the Takeuchi Mining Company was founded. By 1917 there had been rapid expansion including the establishment of a separate division, the Komatsu Ironworks, which was set up to develop and manufacture mining equipment.  The Komatsu Ironworks became Komatsu Ltd in 1921, a stand-alone company whose focus was the design and construction of machine tools, presses, pumps and agricultural equipment.

Komatsu’s first track type tractor, the model G25, was launched in 1931 and was a design that drew heavily on the Caterpillar 2-ton, examples of which had been exported to Japan by the American Holt company some years beforehand for use in agriculture.  Komatsu engineers studiously examined the Holt 2-ton and re-engineered it to metric, rather than imperial sizes, then manufactured one of their own, the G25 being the result.

During World War II, Komatsu manufactured anti-aircraft shells for the Imperial Japanese Navy and also produced a new track type tractor, the model G40, which was widely used in airfield construction and as a tow tractor to move flying boats around seaplane bases.

Following the War, Komatsu started rebuilding and reorganizing its shattered infrastructure and in a very short space of time began building a whole new series of track type tractors, beginning with the iconic model D50A in 1947. Since 1947, Komatsu has gone from strength to strength and is now a major supplier of earthmoving and heavy mining equipment worldwide with manufacturing facilities in several countries.

The super dozer

When Allis-Chalmers unveiled its HD-41 dozer in 1969, it sent a shock wave through the earthmoving industry.  Caterpillar, which was the leading supplier of track type tractors at the time, had nothing of comparable size or weight (unless you counted their side-by-side D9G which was actually two separate D9Gs joined together making a dual machine).

Komatsu, which had steadily been gaining ground in track type tractor sales throughout the 1960s, took great interest in the HD-41 with ambitions of manufacturing an even bigger machine and taking on Allis-Chalmers at their own game and at the same time stealing a march on Caterpillar.

With an enormous challenge ahead of it, Komatsu engineers took over five years to come up with a suitable working prototype, the end result of which was the model D455A.  One of the first challenges was to find a suitable engine to power the beast as Komatsu at that point, did not manufacture any engines with enough raw horsepower to move a machine as large as the D455A.

Since 1961, Komatsu had been in a cooperative partnership with the USA-based Cummins Engine Company and various models of Cummins diesel engines had been used in a lot of Komatsu equipment.

Cummins technical wizards suggested Komatsu use one of its turbocharged V-12 model VTA1710 engines which had a 620 flywheel horsepower output, which Komatsu engineers considered more than adequate for the new tractor.

Komatsu mated the Cummins powerplant to a split power system of its own design featuring two torque converters and two four-speed powershift transmissions which spread the loading via a centre clutch.                  This meant that each track was powered individually making maximum use of the power available.                  Steering clutches were oil cooled and hydraulically boosted.

The D455A rode on a seven-roller undercarriage of conventional design, pinned to the tractor frame just in front of the sprocket by a massive pivot shaft.  Two carrier rollers per side were used and the tracks were 37-section with sealed links.  Thirty inch track shoes were standard with other widths offered as options including a cast manganese steel version for particularly heavy going.  For such a big tractor the D455A was no slouch, being capable of a nine-mph top speed. The operator was provided with boosted controls and a reasonable degree of comfort and visibility, most units being fitted with a cab.

The Komatsu D455A was officially launched for sale in 1974, the machines target market being heavy mining and large quarry and earthmoving projects.

Usual attachments were either a 16-foot wide, straight bulldozer blade or a 20-foot wide U-blade that could move some serious amounts of material and was ideal for land reclamation, stripping or stockpiling operations.  Komatsu also designed and built what the company called a ‘giant ripper’ for the rear of the tractor. This ripper, in its single shank configuration (the type most commonly fitted), had a ripper tip velocity approaching that of dynamite making it extremely cost-effective for heavy ripping duties.                                    Bare, a Komatsu weighed approximately 58.5 tons and over 90 tons fully equipped with U-blade and ripper.

Sales of the new ‘super-dozer’ were quite good, examples being exported from Japan all over the world. The D455A was particularly popular in the USA, Australia and Russia and in mainland Europe, examples being operated in quarries in Spain and Germany.

In the early 1980s, some updates were undertaken to improve the machines performance, resulting in a new version of the D455A, the D455A-1. These changes included raising the engines horsepower rating from 620 to 650 flywheel horsepower, and a major redesign of the cab and external ROPS frame. These last changes gave the operator enhanced visibility as well as improving access to and from the cab. This was the final version of the Komatsu D455A

In 1984, Komatsu announced a new super dozer, the model D475A. This new machine was designed and built from the ground up on a modular basis making it much easier to maintain and also move from job to job if necessary. Despite having a new successor, the former D455A-1 was manufactured right up until 1987 when it was finally supplanted in Komatsu’s product range by the Komatsu D475A-2.

For the model collector

There has been only one model of Komatsu’s D455A issued and that was by Diapet of Japan. This model is to 1:50 scale and represents an early production D455A, equipped with a straight blade, single shank ripper and external ROPS over a soft cab.  Fortunately for collectors, Diapet did a very good job of capturing the real machines brute size and presence and it also has metal tracks. The only downside is that the model was discontinued some time ago and is becoming a little difficult to find, but they do pop up on Ebay now and then.


Brief specifications – Komatsu D455A-1

Engine: Cummins VTA1710-C800 V12 diesel rated at 650 flywheel horsepower at 2000 rpm.

Transmission: Komatsu-designed dual path type featuring two torque converters and two four-speed. powershift transmissions.

Top Speed: 9 mph.

Steering: Wet steering clutches and brakes.

Track Frame: Seven-roller with 2 carrier rollers per side.

Track Gauge: 8’ 7”.

Track Chain: 37-section, sealed.

Std.Shoes: 30” single grouser.

Ground Press: 14 psi.

Length: 36’ 6” (with standard S-blade).

Width: 15’ 8” (with standard S-blade).

Height:14’ 6”.

Op. Weight: Over 90 tons fully equipped with blade and ripper.