mounted engine which despite the total weight
just exceeding 16 tons gave the machine a top
speed of 12mph. This very heavy machine had
minimal ground clearance and would no doubt
have proved diffi cult to control either off-road
or on hills. These fi ve examples remained in
the United States and were used by the Coastal
Artillery Service.
Devising a way to make such a heavy weapon
mobile would always be challenging, but it
seems this problem was resolved when the
company of Holt (now known as Caterpillar)
designed and built a fully tracked chassis as
a platform for an anti-aircraft gun. Powered
by Holt’s four-cylinder 75hp engine, the model
55-I had a length of just under 21ft, was 10ft
wide and a top speed of 5mph. This speed
may seem a little ponderous but the concept
was innovative, and it was the fi rst American-
designed self-propelled gun on a tracked
chassis. Unfortunately, it arrived too late in the
war to see action.
In an attempt to develop a mobile weapon
similar to the De-Dion, the US Ordnance
Department contracted the New Britain
Machine Company of Connecticut to design
and build a mount for the Model 1916 fi eld gun
which was then sleeved to take the smaller
French 75mm ammunition round.
The truck chassis selected to carry the
gun was the highly respected two-ton White
Model TBC. Positioning the mounting directly
above the rear axle allowed greater travel for
the guns 33in recoil enabling it to be fired
almost vertically. To make the gun platform
level the front wheels were chocked intoposition on metal ramps and to improve
stability four outriggers were positioned at
the rear of the truck.
The gun had seats for four crewmen and
there would be a similar number of crew who
would stand on the ground to load and set
fuses. There was no provision for carrying
ammunition, equipment or more than two of
the crew, so there would have been a second
truck for this purpose.
Sadly, there are no photographs of these
machines in action as shortly after the
fi rst White gun trucks arrived in France the
Armistice was declared and the need for
them evaporated. Just 51 were ordered and
photographs show one of them being tested
at the Paris Ordnance Depot on November 9,
1918, additional ones lined up at St Nazaire
docks and rather sadly a room full of unissued
gun trucks at the New Britain Machine
Company factory in January 1919.
Just after the Armistice was signed the
French took back all of the guns they had
loaned to the AEF, leaving them with just the
two purchased De-Dion gun trucks, the newly
arrived Whites and the 50 gun mounts built to
take the French 75mm gun. The mounts were
thought to be useless though and were
immediately scrapped. Although the American
AA Service established an average kill rate of
one aeroplane for every 605 rounds fi red,
throughout the entire war not one enemy plane
was shot down by an American manufactured
gun. When it came to the manufacture of AA
artillery the US Ordnance Department really had
provided too little, too late.Without its gun in place the Holt 55-I looks rather
unusual, but it was the United States fi rst fully
tracked gun platformEven with its signifi cant weight the Holt had
outriggers to stabilise the gunThe 3in gun mounted to the Holt 55-I could fi re a
15lb shell a distance of over fi ve milesThe Holt 55-I had tiller steering and the driver
certainly appears to be enjoying taking this unusual
machine for a drive
‘The fi rst
American troops
landed in France
in June 1917’
Carrying the ammunition and crew
for each De Dion-Bouton gun truck
was a De Dion-Bouton Auto CaissonBefore going into action the White is driven up two metal ramps to create a level fi ring platform