THE CREWE TRACTOR
"We often discover what will do by finding out what will not
do; and probably he who never made a mistake never made a
discovery."
SMILES.
A year or two prior to the war, the present writer remembers one
occasion, in particular, on which he was discussing with a friend,
possessing considerable knowledge and experience, the well-worn subject
relating to the merits and demerits of the various leading "makes"
of motor-cars. To a direct question as to what particular "make" he
considered as being _the_ best _par excellence_ came the somewhat
startling reply, "The Rolls-Royce and the Ford." Whether at the
period referred to, and with expense no object, the average intending
purchaser would have "dumped" for a Ford with the same enthusiasm as
for a Rolls-Royce must remain an open question; suffice it to say that,
comparisons remaining, as they always have been, distinctly odious,
the two examples of automobile science just mentioned have, during the
Great War, each in their respective spheres, performed prodigies of
prowess, the Rolls-Royce more particularly in the matter of important
Staff work, as well as in armoured car activity, the Ford in a variety
of rôles, embracing the functions of anything from a compact and speedy
little motor-ambulance to a water-carrier in the wilderness.
One _rôle_ allotted to the Ford, however, although of necessity
accorded little or no prominence in the public Press at the time,
proved far-reaching in its effects in regard to practical utility from
the strictly military point of view.
Without in any way paralysing its _fons et origo_ as a road vehicle,
but embodying all the potentialities of a light-railway engine, there
was evolved from a simple Ford chassis an entirely novel and mechanical
species of animal, which one might almost say combined the respective
physiologies of the proverbial hare and tortoise, and which in due
course was christened the "Crewe Tractor."
The brain-wave to which this cunning little contrivance owes its
existence is directly attributable to the inventive genius of one of
Mr. Bowen-Cooke's talented daughters, and the incidence of the project
almost whispers of romance, in that a chance encounter, a _rendezvous_
continental and cosmopolitan, a cup of coffee, and an exchange of
confidences, duly culminated in a conception which had as its outcome
a very perceptible reduction in casualties, the percentage of which,
at least in one particular respect, had tended to reach a figure
lamentably high.
On the occasion in question, towards the end of 1916, having as her
_vis-à-vis_ a British officer (on leave in Paris at the time), Miss
Cooke was digesting a dissertation on the inherent difficulties,
dangers and fatigues to which men were incessantly subjected when
relieving one another in the trenches; by day, an open and exposed
target to alert enemy marksmanship; by night a prey to pitfalls,
victims to unnumbered and water-logged shell-craters, in which,
encumbered with personal impedimenta, they were often engulfed, never
to appear again.
Obviously the easiest solution would be a means of transit, a tiny
metal track, ubiquitous, traceable under cover of darkness across the
trackless waste, with diminutive rolling-stock available at any point.
But how to achieve this end? No one could deny but that the need was
both immediate and pressing.
Seemingly happy inspirations, as all the world knows, succeed more
often than not in theory rather than in practice, and for this reason
all credit is due to Miss Cooke in that the happy notion of utilising
a Ford car, pure and simple, and of converting it into a light railway
tractor materialised in as short a space of time as is humanly possible
to convert thought into being, to fashion fact from fancy.
Moreover, the advantages accruing from the idea were not limited to
this one extent only, for quick to perceive the essential, Miss Cooke
further devised a scheme whereby the vehicle, remaining entirely
self-contained, was both convertible and re-convertible; that is to
say, like the hare it could speed along the high-road to any given
point or locality, where quickly transformed it would, like the
tortoise, commence its slower and uneven progress on a diminutive line
of rails, laid haphazard across some devastated area, unballasted,
lop-sided, up and down, this way and that way. _Per contra_, its
immediate task accomplished, and in proportion as the exigencies of
modern strategy demanded further changes of _venue_, off would come the
little tractor from its erst-while _voie-ferrée_, and shodding itself
anew with road wheels and rubber tyres, away along the high-road once
again to its ensuing sphere of tortuous rail-activity.
[Illustration: A CREWE TRACTOR IN ROAD TRIM.]
[Illustration: A CREWE TRACTOR AS LIGHT-RAILWAY ENGINE ON ACTIVE
SERVICE. [_To face p. 130._]
At first sight the casual observer might reasonably have been excused
for puzzling his brain as to the exact nature of the contrivance,
curious if compact, and neatly secured on the familiar Ford chassis.
But on closer inspection, the salient features would resolve themselves
into a fairly obvious entity; nor should a due meed of praise be
withheld from the draughtsmen and engineers responsible for the
successful evolution of the tractors on a sound and practical basis.
At the outset, considerations such as height of centre of gravity
contingent upon the loads likely to be carried over an uneven, narrow
and diminutive track measuring but 1 foot 11-5/8 inches wide, length of
wheel-base and corresponding ability to safely negotiate sharp curves,
available tractive effort depending upon a coefficient of sliding
friction between tyre and rail, all these appeared as obstacles not
altogether easily surmountable.
Official cynicism, too, coupled with an amount of adverse criticism,
had, perhaps not unnaturally, to be faced and met. How for instance
could a "flimsy" Ford chassis be expected to withstand loads and
stresses for which evidently it had never been designed? Unlike that
Government, however, which "foresaw nothing and only discovered
difficulties when brought to a standstill by them," Mr. Cooke, with a
quiet assurance bred of innate knowledge and experience, could well
afford to go ahead "on his own"; official disdain should wait and
see. Probably but few were aware for example that, whereas in regular
locomotive practice a tensile strength of twenty-eight tons per square
inch is considered ample margin for special axle steel, the "flimsy"
Ford is built up of Vanadium steel, having a tensile or breaking
strength of no less than seventy-five tons per square inch!
The somewhat undue height of a Ford chassis for light railway purposes
was a preliminary problem to be tackled, and it was decided to
substitute the driving road wheels with sprockets and perforated steel
rail-wheels, drop-forged with flanges. The question of a suitably short
wheel-base was quickly determined by the introduction of a pressed
channel steel underframe of 5/32 inch plate on which the Ford chassis
was secured; the leading and driving rail-wheels and axles being so
arranged that a rail wheel-base of 4 feet 5 inches was obtained, as
against the 8 feet 4 inches wheel-base of the road-chassis.
Radius rods ensured a nice adjustment of the driving chains, and as
a measure of precaution against any possible failure of the Ford
back-axle supplementary band brakes of generous dimensions were fitted
to the driving rail axles, these being additional to the standard
Ford brakes. A "skefko" type of ball-bearing fitted to the original
tractors, had perforce to be superseded by brass floating bushes
owing to ever-increasing demands in connection with the manufacture
of aeroplanes. These bushes were merely a temporary rather than a
permanent substitute, for very speedily there was introduced an
approved type of roller bearing, which, thanks once again to the
ever-ready adaptability of the fair sex element in Crewe Works, was
duly forthcoming in all-sufficient quantities, and of a quality leaving
nothing to be desired.
Numerous experiments were carried out with a view to determining a
rail-wheel diameter calculated to give the most satisfactory results.
It was assumed that the average Ford car attained a maximum degree of
efficiency when running at a speed of 25 m.p.h. with the engine turning
over at 1500 r.p.m. With a diameter of 2 feet 6 inches at the tread of
the tyres, the road wheels and back axle would be revolving at the rate
of 280 r.p.m. A further calculation went to show that with sprockets
having a gear ratio of 30 to 40, and with the rail-wheels having a
diameter of 18 inches, the latter would revolve at the rate of 210
r.p.m. as against the 280 r.p.m. of the Ford back axle, this resulting
in the tractor averaging a speed of 987 feet per minute, or 11 to 12
m.p.h. which was considered adequate and suitable for the varying
conditions to which it was likely to be subjected.
In addition to ensuring a systematic means of transport for men
proceeding to and from the trenches, the Crewe tractor was further
requisitioned for taking supplies of ammunition to artillery
emplacements in the forward areas. Suitable trolleys were attached,
and the little tractor, prior to going into commission, was required
to prove itself capable of hauling a dead-weight minimum load of 5
tons, not only on the level, but on an upward gradient of 1 in 20,
halfway up which gradient it was further required to stop and re-start,
there being in Crewe Works a track specially laid for the purpose
of subjecting every tractor to this crucial test. It was found, by
experiment, that by doubling the diameter of the trolley wheels, from
7 inches to 14 inches in diameter, double the load could be hauled.
"Slipping," an inherent difficulty due to greasy rails, had to be
reckoned with, and was in no small measure counteracted by the addition
of a central driving chain, coupling rear and front axles through the
medium of sprockets. The frictional resistance (_i.e._ the force at the
rails when the wheels are on the point of slipping) was found to be 448
lbs. with a load of 1 ton on the carriage of the tractor, this being
sufficient to enable the tractors to pass the required test. The Ford
transverse rear spring was supplemented by two helical springs placed
vertically between the Ford and tractor frames.
To obviate the necessity of turning at the various termini of the
track, and to enable the tractor to always proceed in forward gear,
an ingenious method was devised, whereby, with the aid of a screw and
ratchet, working on a transverse beam and socket laid across the rails,
the tractor was raised bodily clear of the rails, and swung round,
ready to proceed in the opposite direction.
Fitted with a high gear, several tractors were specially adapted for
inspection purposes; in short, the extent of the ubiquitous utility,
and of the universal popularity of these remarkable little machines,
may be gauged by the fact that their appearance was welcomed on fronts
as divergent as were those of France, Macedonia, Egypt, and Mesopotamia.