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The light railway manuals of all the Allied armies specified a depth of ballast of 6 in., extending at least 6 in. beyond the ends of ties, and noted broken stone as the most suitable material. This required about 1,000 cub. yd. of stone for each mile. Of course no such amount of material could be brought up by the line itself during rapid construction, even if it had been available in rear. Whatever was available locally was used.

Speed of construction varied greatly according to conditions. On the construction of a line between Abainville and Sorcy (28-5 km. of heavy work) it was found that 1,758 man-days were re- quired for the construction of one mile. During the progress of this piece of work, 2-69 m. of track were built in a few minutes over half a day. The entire force engaged was 2 officers and 135 men, 2 locomotives and 2 motor-trucks. The work was in rear of a quiet sector of the American front, the conditions not being very different from those of peace. On four short tracks con- structed to connect American and German 6o-cm. lines after the battle of St. Mihiel (total length laid in all 19 km.), 2,012 man- days of work were required per mile. French experience indicates that this latter figure is about what is to be expected under favourable conditions. British figures vary from 1,760 to 2,400 man-days per mile. These figures may be compared with 4,300 man-days of work required in the construction of a standard- gauge line, following light-railway methods, between Varennes and Grandpre during the American Meuse-Argonne offensive.

French " soixante " track consisted of rails weighing from 15- to 19-lb. to the yard, made up into sections, 5 metres, 25 metres and ij metres long, the steel ties being riveted to the rails. When riveted sections became bent or broken, they could not be repaired in the field. For this reason the Americans adopted a fabricated section, in which the ties were fastened to the rails by bolts and clips. If a section became bent or broken, the ties could be removed, the rails bent back to line and new ties substituted. The American rail weighed 25 Ib. per linear yd., and came separately in 30- ft. lengths for laying on wooden ties as well as in fabricated sections. A mile of American track (fabricated sections) weighed a little over 75 tons, while a mile of track on wooden ties weighed about 90 tons, but where the wooden ties were cut in the forward area, the actual material from the rear weighed but 43 tons. The British used 2O-lb. rail, and both British and Americans favoured the track made with separate rails laid on wooden ties. Fabricated track, however, was of great value in laying temporary lines and particularly in forward areas, as a damaged section could be removed and replaced in the dark and without much noise.

The German equipment-track came in 10- and ig-lb. rail, but they too made much use of the separate rail, wooden tie construction. On their main arterial lines on the Verdun front a great part of the rail weighed upward of 30 Ib. to the yard, a considerable amount being very heavy rail taken from standard-gauge lines which could not be operated so far forward. The Germans made wise use of the standard-gauge track and roadbed for these narrow-gauge lines. By merely moving one rail over to 6o-cm. gauge, they could use the light rolling-stock and, if need came, the standard track could be promptly reestablished. This, however, proved to be a distinct advantage to their enemies when they came to reconstruct captured lines for standard-gauge operations.

The American 6o-cm. motive power consisted of lo-wheeled, 2 6 2, side-tank steam locomotives, with a weight on driving wheels of 12 tons (17-5 tons total) and 6,225 Ib. tractive effort; and gasoline tractors of o 4 o type, weighing 7 tons and 4 tons rated at 50 and 35 H.P. respectively. By actual field tests, the pulling power of these engines on various grades was determined to be (in gross tons) as follows :

Compensated Grade in %

Steam Loco.

50 H.P. Gas. Loco.

35 H.P. Gas. Loco.

High Gear|Low Gear

High Gearl Low Gear

o-o

I-O

2-0

3-0

3-5

258 133 86 61

54

62.5 32-5

2I-O 15-0

I.V"

125

65 42 3 26

31 16

62-5 32-

21 15

The steam locomotive was powerful and gave valuable service on first-class track. It derailed and turned over very easily, owing to its lack of flexibility and very high centre of gravity. The French Pechot, having low centre of gravity and pivoted truck, was able to take curves with ease. It was not so powerful (tractive effort 5,060 Ib.) as the American engine, but it stayed on the track. The German eight-wheeled, o 8-^-0 locomotive had a total wheel base of 7 ft. 4^ in., as compared with the American 5 ft. 10 in. driving- wheel base and total wheel base of 15 ft. 7 in. It weighed approx- imately the same, 18 tons, but all the weight was on the drivers. There was little overhang and the centre of gravity was low. A

flexible arrangement of end drivers gave radial action on curves. While not armoured, the cabs were low and well protected. The four-wheel well-tank locomotive of the Germans had a wheel base of but 3 ft. 7i- in., permitting its use on very sharp curves. The British armies used four or five types of steam locomotives. The Hunslet, 4-76 o, seemed to have given best satisfaction. The weight on drivers was 12 tons; total weight 16 tons.

Of gasoline tractors the French had several types, the principal ones being the Schneider o 6 o, and the Crochat (petrol-electric) o 44 o. The Schneider, which was equipped with a 65-H.P., 4-cylinder, 4-speed engine, compared favourably in pulling power with the steam locomotives. In part, at least, the success of this tractor was due to superior workmanship on the motor and clutch, which was of the three-disc type, and the skill of the operators. The four speeds and low centre of gravity made it suitable for work of all character. The Crochat was completely armoured. The German gasoline tractors were of two types, o 4 o and o 6 o. In general construction there was little difference between them, the outstanding features of both being low construction and little side overhang. Lubrication was supplied to all moving parts from local sight feed reservoirs or from a mechanical lubricator in the cab. The planetary transmission was controlled by a hand-wheel in the cab, and the operator could apply the power gradually. No effort on his part was required to hold the power at a certain stage of engagement, as is necessary with the clutch and spring action. Simple engines, low speed, heavy fly-wheels, smooth and positive application of power, were the great points in the German tractors.

The American rolling-stock was heavier and of greater capacity than that of other armies. For long hauls on fine track this was of advantage, but the " soixante " was not intended to be a long haul, heavy-traffic railway. British cars were relatively light and flexible, but included more types than those of the other armies. The German equipment was the lightest of all. Their gondola was made by attaching removable sides and ends to a flat car. One end only of their tank car was provided with roller side-bearings enabling it to run on uneven track. The tank cars of other armies derailed frequently because of lack of flexibility between the trucks.

The " soixante " lines were operated by a simple system of telephone dispatching, adapted from the Manual Block System. The railway was divided into several dispatching districts, each controlling from 25 to 75 km. of track. Control was exercised by telephone through operators stationed along the line at intervals of from 3 to 5 kilometres. At advanced points, where night operation alone was possible, and during extensions, temporary operators equipped with portable field telephone sets kept in touch with the permanent operator next in rear or with a special dispatcher.

The general superintendent of a system was connected by tele- phone with all the dispatching districts, and all orders for the movement of supplies and personnel were handled through his office. He also arranged for the proper distribution of motor-power and rolling-stock among the several districts under his control in proportion to the relative traffic requirements. (G. R. S.)

Pioneer Railways in the Middle East. In the World War, the development of standard-gauge lines in the western theatre was so high that " pioneer " lines were totally unnecessary. Much work was done in creating new sidings, short loops and the like, but owing to the nearness of the sources of supply, the quantity of labour available and other causes, all this work was rather accelerated normal work than pioneer building proper.

In the eastern theatre of war, too, most of the work done in Russia was rather a speeded-up development of the normal rail- way system than pioneer work, except in the case of the railway between Murmansk and Ivanka (Zuanka). Work on this line, however, was carried out by the civil authorities and under peace conditions and it can hardly be called a military pioneer railway.

In two theatres, however, the pioneer railways were construc- ted in immediate connexion with operations, and the work done in these two theatres must be considered in some detail, both as an illustration of military railway principles and as an important element in the history of the World War.

Mesopotamia. In no theatre of war was the maintenance of communications so precarious a matter as in Mesopotamia. The rivers during the flood season became hardly navigable, while the constant silt deposits have not only constricted the beds but even raised them above the level of the country on either side the banks. Consequently, hundreds of square miles of land are, in spite of the protective "bunds," inundated almost every year; and railway construction is hampered or made impossible. Moreover, the climate is subject to great extremes. So intense is the- heat during the months of June, July and Aug. that work has to be suspended for several hours each day; while, on the other hand, the mornings and evenings during Dec. to Feb. are so cold that the output of east- ern labour is restricted. Again, it was found that, owing to the peculiar nature of the soil, unballasted surface rail-track often