"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.

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.