ARM: Review -- The D7 Tractor in US Military Service 1941-1953

Book Review: The D7 Tractor: A Visual History of the D7 Tractor in U. S. Ar
my Service 1941-1953 by David Doyle; Ampersand Publishing, Del Ray Beach, F
lorida 2006; 120 pp. with both B&W and color photos; price about US $19.95
(ISBN 0-9773781-8-0)
Advantages: first, good clear reference work on the D7 tractors in US milit
ary service and the fittings applied to them for different functions
Disadvantages: no plans provided
Rating: Highly Recommended
Recommendation: for all WWII and Korean war American military fans
As they always say, "Amateurs talk tactics, professionals talk logistics."
One of those logistic items is the means to provide roads, runways, access
routes, and fortifications for the combat forces when and where needed, an
d that means engineer services.
The Holt Tractor company developed the patented "Caterpillar" track drive
prior to WWI, and its was used for many things such as "Little Willie", the
forebearer of all tanks. In 1925 they merged with the C.L. Best Gas Tracto
r Company to form Caterpillar, and "Cat" has been a major force in construc
tion equipment ever since.
The D7 model was introduced in 1938 as a medium tractor for construction n
eeds: D3/4/5 were light tractors, D6/7 mediums, and D8 and above heavy and
special purpose tractors. Depending on its fittings, it weighed from 16 to
20 short tons in service. Powered by a big four cylinder diesel engine of s
ome 82 HP, the tractor was small enough to be easy to transport but heavy e
nough to be a good maid-of-all-work in service. It should be noted that the
D7 model has remained in the Caterpillar catalogue since that time, and is
still offered in several different versions today. This book covers the fi
rst models of the tractor and how they were used by the military during WWI
I and Korea.
As noted, the D7 was only a tractor, and had to be specially fitted with d
ifferent equipment sets and fittings to perform as a prime mover, mobile cr
ane, road scraper, or most popularly, a bulldozer. David Doyle has gone thr
ough a number of sources and combed the US National Archives Signal Corps f
iles to provide an excellent photographic journal of these vehicles.
The primary fitting covered in the book is the Le Tourneau WCK7 "Angledoze
r" blade, operated via an overhead cable and sheave assembly from a rear mo
unted winch, most commonly from fork lift manufacturer Hyster. This require
d the winch to be engaged to raise or lower the blade. Tilt and angle were
adjusted by manually detaching the blade and reattaching it to different fi
ttings on the support arms, so it could have both angle and cant set for di
fferent functions.
Based on their areas of operation, later on in the war a set of basic armo
r protection was designed and fitted to vehicles likely to come under fire,
and they are covered here in the book as well.
Different versions include use as the power for the M20 mobile crane, Le T
ourneau and Allis-Chalmers scrapers and earth movers, pipe layers, and a sp
ecial beach variant designed by Donald Roebling (of Alligator fame).
The book presents all of these variants in action, and gives a great amoun
t of detail on them showing how the Engineers fitted them out or just hung
things on them when and where needed. Most of the "in action" shots show "j
erry" cans for both diesel and gasoline fuel (the engine was started by a t
wo-cylinder gasoline "donkey" engine started by a hand crank) and a portabl
e grease pump on the running boards.
While many modelers tend to overdo the amount of mud found on tanks, this
book clearly shows that in many places you can't have too much mud on a D7!

The last part of the book is a nice selection of current color photos of t
wo restored US military D7s in use and demonstrated for the public.

Overall this is a bit out of what many armor modelers would consider "main
stream", but the photos show that the over 15,000 D7s purchased by the War
Department were put to good use and in the forward areas with the troops in
every theater of operations.
Thanks to Pat Stansell for the review copy.
Cookie Sewell
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