engineers

engineers use their skills to help their own army live, move, and fight, and to impede the efforts of the opposing side's engineers. Before 1939 they worked largely with pick and shovel, artisan tools, explosives, locally found materials, and conscripted labour. In the Second World War, however, their capacity to affect the course of operations was increased dramatically by the introduction of mobile earth-moving machinery—bulldozers, scrapers, graders, and excavators; by the development of rapid bridging equipment such as the Bailey bridge; by the mass-production of anti-tank and anti-personnel mines; and by the manufacture of prefabricated surfacing materials for the rapid construction of all-weather airfields.

The needs of armies for engineer help increased equally dramatically: the weight and numbers of military vehicles far exceeded the pre-war design capacity of most roads and bridges, even in Europe; logistics became increasingly complicated as the tonnage of supplies to be carried multiplied; the scale of theatres of operations and of battlefields expanded inexorably in step with the return of mobility to the land battle and the addition of the air dimension; and the ever increasing needs of air forces for airfields and fuel supplies, threw a new load on engineer resources. The scale on which engineers worked can be illustrated by the fact that during the Burma campaign alone the Allies built 407 airstrips, 1,300 bridges, and thousands of kilometres of roads which included the Ledo Road, the Tamu Road from Imphal to Kalewa, via Palel and Tamu, and the Tiddim road from Imphal to Kalewa, via Tiddim and Kalemyo.

Engineer units constituted an average of about 12% of most field armies in the Second World War. They were divided broadly into two components: about one-third were field or combat engineers, organic to divisions and corps, who worked in the combat zone, each division having the equivalent of an engineer regiment (800–1,200 men); and the balance were lines of communication engineers, trained and equipped for major engineering tasks throughout the theatre of war. (Electrical and mechanical engineers, employed on repair and recovery of vehicles and equipment, formed part of the logistic organization of armies and were not classed as military engineers.) In addition, there were specialized engineering organizations at national level, set up to undertake strategic tasks: the Todt Organization, which constructed major German fortifications and U-boat bases, using forced labour; the American Seabees, employed to construct forward operating base facilities in support of amphibious warfare operations in the Pacific war; and the equivalent Japanese organizations, which used prisoners-of-war as labour on major engineering projects such as the infamous Burma–Thailand railway. The USAAF, unlike other air forces, did not leave the construction of airfields to army engineers. Instead, it formed its own self-contained engineer aviation battalions (27 officers, 761 men to each battalion) which eventually totalled nearly 118,000 engineers. Lightly equipped parachute engineer battalions were also formed to build emergency airstrips after an amphibious landing.

1. Field engineers

Field engineers had four principal tasks: In defence they helped protect their formations by constructing field fortifications; digging in major weapon systems; strengthening natural barriers like river lines; and creating artificial obstacles such as minefields and anti-tank ditches. In withdrawal they delayed the advance of the opposing side by demolishing roads, railways, and airfields; by scorched earth operations; and by random mine-laying and booby-trapping. In attack they helped the assault forward by breaching natural and artificial obstacles; by destroying fortifications impervious to artillery fire and air attack; and by clearing routes forward through the battle zone. In advance they opened up routes forward by bridging water obstacles and dozing through dry ones; by mine and booby-trap lifting; and by clearing roads through the rubble of bombed towns and villages, or making diversions around them.

In addition they had the logistic tasks of supplying water to forward troops, and of constructing or renovating living accommodation for them when this was needed, particularly during winter.

The Second World War saw the rapid development of techniques by field engineers in the combat zone.

(a) Fortifications

When the war started in 1939 both sides in Europe were placing great faith in the steel and concrete fortifications and obstacles of the Maginot and Siegfried Lines on the Franco-German frontier, already built by civilian contractors under the supervision of military engineers and almost regardless of cost. Neither was ever fully tested in battle because the Maginot was outflanked by the German blitzkrieg through the Low Countries in June 1940 (see FALL GELB); and the Siegfried could not be manned properly by the weakened Wehrmacht when the Allies crossed the German frontier in the autumn of 1944.

In the Far East, the Americans placed similar faith in the efficiency of steel and concrete in the defence of Corregidor in the Philippines, and the British did so to a lesser extent in Singapore. Both fell relatively easily to the Japanese.

Although fixed fortifications can deter assault, they have one exploitable weakness: their immobility. An attacker can examine them in detail, devise special equipment and methods for breaching them, and do so by concentration of effort at the weakest point. For instance, the key to Belgium's defences, Fort Eben Emael, was captured by the Germans in May 1940 by the novel use of gliderborne assault engineer troops, landing inside the fortress and using hollow charges (see demolition, below) to neutralize the defences.

On the Eastern Front Soviet engineers had few equals when it came to turning whole towns and villages into fortresses and they showed great ingenuity during the German–Soviet war. Houses were converted into blockhouses, cellars became strong-points and bunkers, and sewers were used for communications and for infiltrating behind German lines. So strongly and skilfully were the defences constructed that only street-fighting, which included ‘mouse-holing’—moving from house to house by blowing holes in the party walls—and the use of flame-throwers, overcame them. As a consequence it was common for Soviet and German engineers to be in close combat against one another.

The most successful defensive lines in the Second World War were those constructed by field engineers during operations in positions where the front had already begun to congeal. The best examples were the Soviet defences in front of Moscow and Leningrad in 1941, and the German Gustav Line in Italy, based upon Monte Cassino, in 1943–4. Winter weather contributed to the successful consolidation of these lines.

Nevertheless, pre-planned strategic defence lines still had value in forcing attackers to manoeuvre and concentrate. Lines constructed after the outbreak of war comprised a mix of reinforced concrete bunkers, gun emplacements, and anti-tank obstacles, usually built by civilian contractors under military supervision, and field works—trenches, anti-tank ditches, barbed wire, and minefields—constructed and laid by field engineer units. Examples of these were the anti-invasion beach defences of southern England in 1940–1; Hitler's much vaunted Atlantic Wall in 1943–4; the German Hitler and Gothic Lines built during the Italian campaign in 1944; and the Japanese defences of their fortified islands in the Pacific in 1943–5.

The stalemate of trench warfare, which engulfed all fronts in the First World War, was hardly known. The lethal combination of machine guns and barbed wire had been neutralized by the advent of the tank, and in their place came the lavish use of anti-tank and anti-personnel minefields, but these could only hinder and not stop a determined attacker as was shown at the second battle of El Alamein in October 1942 and during the Normandy landings in June 1944 (see OVERLORD).

(b) Demolition

In the face of the German blitzkrieg, the Allies' standard demolition equipments and techniques, inherited from the First World War, were soon shown to be too slow and inefficient during their enforced withdrawals in the Norwegian campaign and in the fighting which preceded the fall of France in June 1940; in the Balkan campaign in 1941; and in the Burma campaign in 1942. In consequence, Rapid Demolition Devices (RDD) were developed by the British, in which speed rather than economy of explosives was the primary consideration. The principle of the hollow charge was used in the ‘Beehive’ device (see explosives), which punched a deep hole into masonry, thus eliminating the tedious process of pneumatic drilling when placing borehole charges. The same principle was used for linear-shaped charges, called ‘Hayricks’, for cutting the steelwork of bridges or reinforcing bars in concrete structures. And crates of bulk explosive, which could be slid rapidly off the backs of vehicles, were designed to sever bridges. Plastic explosive, which could be quickly and easily moulded to fit tightly round targets of any shape, was also introduced. RDD were not available before the Allies went over to the offensive at the end of 1942, but they were further developed for combat engineers to attack the concrete defences in Hitler's Atlantic Wall and the fortified Channel ports.

The German withdrawal operations after the tide turned against them in 1943 were on a far larger scale than the earlier Allied retreats and lasted far longer. Their engineers had ample opportunity to refine their demolition and scorched earth techniques. Their long withdrawal in Italy, which started from Salerno in the autumn of 1943 and ended in the Po valley in the spring of 1945 (see Argenta Gap), was a classic demonstration of the use of explosives, booby-traps, and mines to delay a more powerful opponent. Almost every bridge and culvert on Italy's north/south roads, and on all the many river lines, were not only blown, mined, and trapped, but were usually covered by the tanks or self-propelled guns of their rear guards to impose increased delay.

(c) Mines

For the types of mine used on land, and the techniques developed for laying and clearing them, see mine warfare, 1. Mine warfare was fought by opposing field engineers in all theatres of war, but most intensively in the deserts of North Africa and on the Russian Front where natural obstacles were scarce.

As in naval mine warfare (see mine warfare, 2), there was a constant battle between the engineers on both sides as new types of mines, fuzes, and laying techniques were devised by the defenders to defeat the advances in detection and clearance methods of the attackers.

(d) Assault Engineering

Engineer troops, using explosives and obstacle crossing devices, have always played a major role in attacking fixed defences, but in the Second World War this role was carried a step further by the British development of armoured assault engineer units. They were equipped with five main types of modified tanks:(i) Flail tanks were developed first. They were designed to clear lanes through minefields, using a rotating drum, fitted to the front of the tanks, which flailed the ground with weighted chains to explode any mines in their path. They were first used with success at El Alamein (Figure 1).(ii) Tank-dozers tanks fitted with bulldozer blades for filling in ditches and road craters, and clearing away other obstacles under fire (Figure 2).(iii) Arks: turretless tanks, decked over and fitted with movable ramps, front and rear, which could drive into an obstacle and lower their ramps, thus providing bridges for tanks and other vehicles to cross over their backs (Figure 3).(iv) Bridge-laying tanks these carried scissors-type bridges nested on their backs, which could be opened up to their full length and lowered hydraulically over gaps without the crews leaving their armoured protection.(v) AVREs (Armoured Vehicles Royal Engineers): tanks fitted with demolition guns, firing 18 kg. (40 lb.) projectiles, carrying 12 kg. (26 lb.) explosive charges and nicknamed ‘flying dustbins’; and equipped with special fittings to allow them to carry a variety of engineer devices such as fascines for ditch crossing, frames holding made-up demolition charges for breaching concrete obstacles, and dozer blades for rubble clearance. They were also fitted with side doors so that crews could get out to place demolition charges by hand if need be (Figure 4).

For the Normandy landings the armoured engineer units were grouped in the specialized 79th Armoured Division under Maj-General ‘Hobo’ Hobart, who was charged by Churchill with developing ways of overcoming the Atlantic Wall defences. Armoured engineers were also employed in Italy in autumn 1944, breaching the Gothic Line and crossing the successive river lines in the Romagna during the Allied advance towards the Po valley.

US and Soviet engineers used several very similar equipments, but the Germans and Japanese did not: they were on the defensive by the time the requirement was recognized.

(e) Bridging

Significant strides were made during the war in speeding up military bridging. The greatest success came with the invention of the British Bailey bridge by Sir Donald Bailey of the Military Engineering Experimental Establishment at Christchurch, Dorset (Figure 5).

The Bailey bridge girders were constructed from a series of identical steel lattice panels held together by high-tensile pins at their four corners. Each girder could be doubled or tripled for extra length and strength, and could be given up to two extra storeys for very large spans. The roadway was supported on lateral transoms, carried on the lower chords of the panels, and the whole structure was launched on rollers, using a counterweight, over the gap to be spanned. It was first deployed operationally during the North African campaign in Tunisia towards the end of 1942, and became the main dry bridging equipment of the Allied armies.

For bridging rivers, two distinct families of floating bridges were developed. The British and the Soviets retained the traditional wooden pontoons to support their bridges, while the Germans, Americans, and Japanese favoured more vulnerable, but easily transported, inflatable rubber floats. The British used their Folding Boat Equipment (collapsible wood and canvas boats, carrying an easily constructed roadway) for vehicles up to 9 tons, and Floating Bailey (Bailey bridging carried on pontoons) for loads up to 70 tons. The Americans used Treadway bridges, which consisted of linked wheel tracks carried on various sizes of pneumatic pontoon, depending on the load to be carried. Sections of most floating-bridge equipments could be modified for use as rafts.

The British lagged in one aspect of river-crossing equipment. They relied on flimsy canvas folding boats, paddled by hand, to carry assaulting infantry across rivers to establish bridgeheads, whereas other armies used powered light alloy or pneumatic storm boats.

River-crossing techniques of the Western Allies during the Second World War were brought to their apogee during their successful Rhine crossings in March 1945, by which time the speed and efficiency of Soviet engineers in developing bridgeheads across their rivers had also been proven as a German Army Group South report of September 1943 illustrates: ‘During the retreat across the Dnieper on either side of Kiev, German engineers and bridging formations built seven bridges in a sector 650 km. (400 mi.) long over which the German troops were to withdraw. The Soviets, on the other hand, constructed in short time 52 bridges and foot-bridges across 400 km. (250 mi.) of the river.’

(f) Route Clearance

In the First World War, the countryside beyond the pulverized area of the front line was almost untouched by war and presented few problems to advancing troops once they had broken through. This was far from so in the Second World War. Routes forward were not only obstructed by the other side's demolition and mine-laying operations, but also by the destruction of towns and villages by the air forces. Such was the damage done that all field engineer resources often had to be concentrated upon opening up just one route forward per division. Once winter weather set in and mechanized armies became roadbound, the ability of their engineers to keep routes open became a limiting factor in operations.

2. Lines of communication engineers

Lines of communication engineer units were largely recruited from civilian firms with specialist engineering skills. They fell into four broad categories: Construction units for construction and maintenance of roads and bridges; of airfields; of fuel and water pipe lines; and of accommodation for personnel and logistic installations such as hospitals, store depots, and workshops. Electrical and mechanical units for the reconstruction of damaged electric power installations and water supply systems, and provision of power and water in base areas. Railway units for the repair and operation of essential railway systems. Port operating and construction units for the development of base ports after naval clearance of sea mines and sunken ships in their approaches.

Most engineer work on the lines of communication required large labour forces. The western Allies depended upon recruiting local civilian labour and raising military pioneer units, but the Axis powers and the Soviets used conscripted labour and prisoners-of-war for labour-intensive engineer work like road and airfield construction.

In the initial phases of the Second World War only the Germans and Japanese were confronted with lines of communication problems, because the Allies were in retreat. Nevertheless, Axis logistic difficulties were never limiting: the speed and success of their operations were such that the infrastructure of the countries overrun was left unscathed and could be used as the basis for expansion to meet increased military requirements.

In the USSR, however, the Germans were faced with the complex railway operating problem of changing from standard to broad gauge at the frontier. They also had to deal with the paucity and poor quality of the Soviet road network. Even the few good roads did not have strong enough foundations to withstand the pounding of German military traffic in the wet weather of autumn before the freeze, and in the thaw conditions of the spring. The Japanese, although needing less logistic support, found monsoon conditions in Burma equally restricting.

When the western Allies turned to the offensive in the autumn of 1942, it was a very different story. Amphibious warfare operations in both the Mediterranean and Pacific theatres of war needed the establishment of bases and airfields on a vast scale, involving a massive effort by their communications engineers; and, as they advanced through North Africa, Sicily, and Italy, and from island to island in the Pacific, they had to overcome the devastation caused by the slow and deliberate Axis withdrawals, while at the same time building up whatever civilian logistic infrastructure remained to meet their military requirements.

The greatest Allied engineer effort of all came with the invasion of Normandy in June 1944. It was the equivalent of moving a city the size of Chicago, USA, or Birmingham, England, across the storm-swept English Channel to a green-field site in France under battle conditions, and supplying it with all the resources needed to fight at high rates of operational intensity. Four engineering feats stand out:(i)The design, construction, placing, and operation of the artificial harbours (see MULBERRIES) on the Normandy coast through which the two Anglo-American Army Groups were supplied with 40% of their requirements until the severely damaged port of Cherbourg was captured and reopened (60% was landed over the beaches).(ii)The rapid construction of airfields in the beachhead from which air cover and offensive tactical air support was provided (23 were built in the British sector alone).(iii)The laying of the PLUTO pipelines across the Channel, which supplied the Allied air forces and armies with fuel.(iv)The subsequent support of the Allied advance across France and into Germany, despite the damage done to communications by the interdiction operations of the Allied air forces and the demolitions carried out by the retreating German Army.

In the same time frame, German engineers were achieving extraordinary feats of ingenuity and improvisation in maintaining the flow of essential requirements to the Eastern, Mediterranean, and Western fronts in the face of devastating Allied air attacks on their transportation system, which were only second in priority to oil targets in the Allied strategic air offensives. No vital rail links were ever severed for long, including the highly vulnerable Brenner Pass line into Italy.

William Jackson