Far more significant pointers were to be obtained from the Spanish Civil War, which broke out in 1936 between left-wing Republican forces and right-wing Fascists, because several nations used it as a proving ground for the latest theories and weapons. At a time when the major navies had embarked on construction of all kinds of vessel from battleships and aircraft carriers to minesweepers and submarines, the meagre Spanish navy, mostly sailing under Republican colours, had little to offer by way of innovation. The sinking of a pre-war dreadnought by Republican bombers taught less than the interesting experience of the British destroyer Hunter when mined on an international patrol intended to enforce non-involvement in the war. Her welded construction was shown to be far more damage-resistant than would have been a rivetted ship. Blockade and counter-blockade, to a large extent applied by aircraft from both sides, by Italian and German submarines on behalf of the Fascists and by minelaying, certainly achieved results although none too thoroughly. Most air attacks were on ships in port with far more hits than those attempted against moving targets at sea where, out of 18 warships attacked, none were sunk. Submarines had their successes and were but slightly deterred by air or depth charge attack. It was only now that the British navy at last came to realize the inherent shortcomings of sonic detection and the inadequacy of Asdic.
Threats from above or below the surface failed to deflect the hierarchy of naval officers, most of whom were gunnery specialists, from according priority to battleships. They concentrated construction upon ships with improved guns, ammunition, protection, range-finding paraphernalia and gyro-stabilized searchlights which would have turned the tables at Jutland. In 1932 France laid down a 26 000-ton battleship; Italy responded with two 41 000-tonners in 1934. Then Germany laid down two 32 000-tonners (announced as 26 000 tons) followed in 1936 by two 42 000-tonners (announced as 35 000 tons). Britain tardily replied to this with two 37 000-tonners in 1937, the same year as the Japanese laid down the two biggest-ever battleships – the 64 000-ton Yamato and Musashi with their 18.1-in guns each firing a 3200-lb projectile. Naturally the USA had to match this threat with a programme of six 35 000-ton ships armed with 16-in guns. All were at vast cost and distractive of other industrial effort, but justified on the familiar grounds of indispensability.
Gunnery addicts might discount the air threat but they tacitly admitted its danger by specifying that secondary armament of battleships and main armament on smaller vessels were to be high-angled for air protection. They also added batteries of multiple 20-mm – 40-mm cannon and multiple machine-guns to deal with low level attacks. And while declaring that aircraft carriers would occupy only an ancillary role to battleships, they initiated extensive aircraft carrier construction, incorporating the experience gained with earlier types. All would mount batteries of anti-aircraft guns and be enlarged, both above and below the flight deck, to carry 70 or more aircraft. Some, like most cruisers and battleships, would be fitted with compressed air operated catapults (long after the American Theodore Ellyson first took off from one in 1912). To ensure the safe return of aircraft at the end of a mission by day or night, all carriers would be fitted with radio homing beacons (of which the British Type 72 DM, successfully tried out during 1931-33, was a prime example despite a tendency to distortion by high-tension electric cables) and, in the case of the British Illustrious class, vitally ahead of the time with a well-armoured hangar and flight deck.
War on land in Spain at first differed little from 1918 for the simple reason that the armies were equipped with the weapons of the First World War. The tanks sent by Italy and Germany were light types armed only with machine-guns because in 1936 neither nation had anything better. Those sent by Russia were superior because, although lightly armoured, both the slow Vickers-type T 26 and the fast Christie-type BT2 were armed with 37-mm guns. Their employment reflected the furious debates then raging between the old and new schools of thought concerning armoured warfare. The old school argued that AFVs should be subservient to the infantry and move at infantry pace, as at Cambrai; the new school claimed that if tanks with accompanying mechanized artillery, engineers and infantry were driven through enemy lines in deep penetration raids (as Fuller wanted) a strategic decision would be obtained. General Pavlov, the Russian in command of Republican armoured forces in Spain, attempted two deep penetration attacks but failed to reach his objectives because the tanks had insufficient infantry and artillery in attendance. General Franco, for his part, insisted on using German and Italian tanks for close infantry support only – and with reason, since light tanks were hardly a dominant weapon.
None of this boded well for the German General Heinz Guderian, who was on the verge of forming three so-called Panzer (Armoured) Divisions composed of all arms with the tank as dominant weapon. It was not only that the reports from Spain seemed to decry the deep penetration concept; they also denigrated the need for wireless to control these fast-moving formations. Guderian was not only a General Staff officer of outstanding drive and vision, but also a signals specialist. He took as his model the series of British experiments between 1927 and 1934 which had progressively and publicly demonstrated the kind of `mix’ suitable for modern, all-arms formations up to divisional level, and had shown how effectively one man could sit in a mobile command post with a short-wave, crystal-controlled radio set and control the movement of a considerable number of tanks by voice. He had seen, too, how on exercises (no matter how unrealistically arranged) these formations could out-manoeuvre and surprise much larger conventional formations. Guderian was completely convinced that radio was the key instrument in making armoured forces function to their full capacity, even if their armour and guns were inferior to those of the enemy. His concept also included an entirely new tactical method in which the tank and infantry element of a panzer division acted merely as the spearhead of infiltration to seize vital ground which the enemy could not afford to surrender. Having seized it, his tanks were intended to withdraw to allow anti-tank guns and infantry to beat off subsequent enemy tank attacks and thus destroy the enemy armour while preserving his own.
In Spain the latest anti-tank guns with 2000 + f/secs velocity demonstrated their ability to knock out all known tanks at ranges up to 600 yards with a 5 to 1 chance of scoring a hit (a much higher accuracy than lower-velocity field artillery). Of course, the existing 20-mm to 47-mm solid shot did not guarantee a `kill’ with each hit. That was reserved for a quite devastating weapon with a pedigree reaching back to the 77-mm anti-aircraft guns which had shot so well at Cambrai. Now it was the latest 88-mm anti-aircraft gun with a muzzle velocity of 2657 f/secs and an armour-piercing shot weighing 21 lb which could wreck any medium tank with 60-mm (let alone 30-mm) armour beyond 1200 yards, and very likely hit it at the second or third attempt. This gun was tried out in Spain.
The moment was near when the 88-mm gun and its counterparts in other armies were the only pieces capable of penetrating at 800 yards the latest heavy tanks. Once the French and British had concluded in 1931 that a mass of fast-moving, lightly-armoured AFVs were unacceptably vulnerable to the smallest anti-tank guns, they stepped up the gun/armour race by embarking on the construction of slower, heavily- armoured tanks which in the 1920s had seemed prohibitively expensive. In the lead were the French. They rejected 70- to 80-ton models in favour of the Char B weighing 32 tons, armed with a turret 47-mm gun and a short, 75-mm howitzer in the hull, and with 60-mm frontal armour which was proof in most conditions against the German 37-mm gun. This, on paper, was a useful machine with a 300-hp engine giving a speed a little under 20 mph. Unfortunately for the crews, the French remained wedded to the one-man turret, first adopted in 1917. This might have been satisfactory when the gunner, who was also commander, had only to load, aim and fire a machine- gun; but once he had to perform those duties with a cannon and also control his driver and, over the radio, other tanks, efficiency decreased. Far more formidable was the British heavy Matilda II tank, ordered in 1938, with its three-man turret, 80-mm frontal armour, 40-mm gun, 174-hp twin engine and 15-mph speed.
As each nation began to expand its armoured forces it met the problems of inferior industrial knowledge and facilities. In 1932 only the British firm of Vickers and the French Renault company could be said to possess an adequate tank-building capacity – and even they were incapable of meeting the sudden demand for mass production employing many new techniques (such as casting of armour) and designs such as regenerative steering. A shortage of experts, technicians and factories delayed the immediate delivery of high-quality, combat-worthy AFVs. Several armies were compelled to buy inferior machines in order to begin training crews. All might have been well given wholehearted desire among service ministries and general staffs to rectify these shortcomings. As it was, armies, and notably tanks, were held quite low in estimation and order of priority for re-equipment. The navies took their traditional share; air forces were given high, sometimes top, priority; and land forces had to make do with what was left over.
Aircraft factories of 1932 were not, in any case, coiled springs primed for dynamic release. The wariness of air forces and civil operators, restrained by economic recession and confused imaginations, was anathema to capital investment. Contradictory theories still abounded in 1936, and were being explored in the skies above Spain. The opinion that civil airliners were readily adaptable as bombers (thus making it easy for Germany to assemble an air force under the guise of her civil airline) died hard. Such adaptations were frequently unsatisfactory if only because a good passenger cabin does not readily convert to a bomb bay, and the mounting of special defensive armament is not efficiently improvised. Yet the Junkers Ju 52 tri-motor transport had its successes in this role. Franco benefited from it tremendously at the start of the civil war when 20 of these aircraft, later joined by nine Italian Savoia SM 81 bomber-transports, ferried 13 523 troops and 570 000 lb of war material from Morocco to Spain to establish the core of the Fascist army and make the revolution possible by over-flying the Republican naval blockade. And on 14th August 1936, before people had awoken to the peril, a Ju 52 planted two bombs on a Republican battleship from 1500 ft, putting it out of action.
The theory that fast, well-armed bombers would survive (particularly if flying in tight formations protected by interlocking fire from their machine- guns) held water at first – but only because the fighters of 1936 lacked the speed to reach them and the, armament to do serious damage. For example, a Russian Tupolev SB-2 twin-engine monoplane with a speed of 255 mph was a difficult target to intercept by an Italian biplane Fiat CR32 with a top speed of 233 mph – although on occasion this feat was performed. Evidence of this sort underlined the widespread opinion of those, such as the British Prime Minister Stanley Baldwin, that `the bomber will always get through’. It was assumed that this technical imbalance would persist and that, in any case, fighter actions would be impossible if their speeds increased much beyond the extant 220-mph mark. A natural reaction was to build bigger, faster and heavily-defended bombers in the pious hope that their existence would deter an aggressor from using his bombers – in much the same way as it was hoped that the possession of gas would deter its use.
In practice, only two nations wholeheartedly created strategic air forces mainly equipped with large, four-engined bombers: the USA and Britain. The former rather drifted into it, as the Boeing 299 of 1934 (which evolved into the B-17 Flying Fortress) was originally conceived as an anti-shipping machine. British specifications of 1936 called for long-range, four-engine bombers, defended by power-operated machine-gun turrets, which could survive in daylight. Russia and Germany also laid plans for a four-engine bomber strategic air force. But the former’s Tupolev TB-3 machine was far too slow and vulnerable for this and mostly achieved fame as a transport for the men of the first-ever parachute assault division created in 1934. Germany abandoned its ambitions for political reasons associated with the Spanish Civil War and technical requirements related to the perennial struggle of naval and land forces to achieve closely coordinated support for their operations.
Germany’s movement towards abandoning a long-range bomber force began in June 1936 when its main advocate, the Chief of Air Staff designate, ex-infantryman General Walther Wever, was killed flying. His successor, ex-artilleryman General Albert Kesselring, not only leaned slightly towards naval, and above all army, support air forces, he was almost at once faced by the need to recast long-term German plans which aimed at being ready for war by 1943. Action in Spain and the aggressive utterings of his C-in-C, General Hermann Goring, compelled Kesselring to rationalize equipment under development and concentrate on machines in readiness for an outbreak of war in 1938 or 1939. The four-engine bomber fleet was incompatible with this time scale. Its viability was also in question as Kesselring reasoned that the low state of the navigational art precluded finding and hitting targets at long range.
So Germany’s air force, like most others, concentrated on twin-engine medium bombers; single-engine fighter-bombers and single-engine reconnaissance machines, plus a few specialized flying boats, sea planes and four-engine, long-range naval reconnaissance aircraft salvaged from the strategic project.
The shape of the next generation of twin-engine medium bombers appeared in the USA in 1932. The Boeing B-9 was a cantilever wing monoplane, all-metal with a top speed of 188 mph and a retractable under¬ carriage – its contribution to improving aerodynamic designs. Almost simultaneously, the Martin company went a stage further with their B-10 which had two 775-hp radial engines, could fly at 207 mph, climb to 24 000 ft and had a range of 600 miles. With fully enclosed crew cabins and bomb bays, along with a rotatable gun turret in the nose, the B-10 allowed for operational efficiency in the cold of extreme altitudes, dependent as it was on skilled aircrew working in as comfortable an environment as possible. Within a few years, bomber speeds in the region of 260 mph were normal, momentarily keeping ahead in 1937 of the latest fighters in service and providing, incidentally, a useful vehicle for high-altitude reconnaissance with machines such as the German Dornier Do 17, equipped with the latest high-definition cameras. But it was the German Heinkel He 111 with a bomb load more than twice that of the Do 17 which made the biggest impression. It hit the headlines when, in conjunction with Ju 52s on 26th April 1937, it was used to pulverize the town of Guernica. A prime example of justifiable tactical bombing of a strongly defended locality this may well be – and successful, too, since Guernica fell without resistance two days later. But to the world it was presented as a callous experiment in the strategic and psychological process of undermining enemy morale through terror. Guernica became the symbol of air power’s crushing influence, and a warning to weaker nations who dared to withstand Germany’s predatory intentions.
In fact, the Germans undertook no deliberate major strategic attacks in Spain, their current doctrine eschewing it as they concentrated more upon the use of fighter-bombers to attack ground targets by low-flying and dive-bombing. The debut in this role of the latest biplanes (and the last in German service) was not entirely a happy one. Against the latest Russian Polikarpov I-15 biplanes (229 mph) and I-16 monoplanes (321 mph), the Heinkel He 51 biplane at a mere 210 mph was cannon fodder, as was the Henschel Hs 123 biplane dive-bomber (211 mph) which on test had exhibited a nasty habit of shedding its wing in the high-speed dive. But formations of nine He 51s, dropping six 20-lb bombs each on fortifications from 500 ft (each machine sometimes flying seven sorties a day) had a stunning effect on enemy troops and convinced the Germans of their vital importance to the army. This conviction was redoubled when they experimented with heavier bombs carried by the Hs 123s and, in 1937, the latest Junkers Ju 87 monoplane dive-bomber. But despite these robust aircraft proving their worth as heavy artillery, it was also realized that if they were to survive, they needed escort fighters of a calibre higher than those which were coming into service.
Although many air forces continued to specify biplane fighters (the RAF took delivery of the Gloster Gladiator, the last of its line, in 1937 and the Italians their Fiat CR42 in 1939) the writing was on the wall for biplanes, even those with retractable undercarriages. It was clear that these aircraft had almost reached the limits of their development and that another revolution was impending. Charles Lindbergh’s solo crossing of the Atlantic in a monoplane in 1927 did more than anything else to overcome prejudice, which was further eroded when nearly all the seaplanes entered for the Schneider Trophy in the late 1920s were monoplanes. From 1927 onwards, monoplanes monopolized the world air-speed record, 300 mph being exceeded for the first time by an Italian Macchi M52 that year. Even so, doubts about fighting monoplanes were not removed until the air war in Spain dispelled the objection that gravitational forces (radial acceleration, expressed as g) precluded violent manoeuvres at high speeds such as were to be expected in the traditional dog- fight of the First World War. High-speed racing fliers of the 1920s had sometimes lost consciousness momentarily when applying more than 4g in tight turns, and their aircraft often suffered structural failures. Experience in Spain indicated that these forces were tolerable up to a point and that, in any case, the tail-chasing dog-fight was but one transient phase in air combat. Most attacks consisted of a fairly direct line of approach prior to opening fire, followed only subsequently by the mad scramble of tail-chasing which seldom ended in a `kill’ because it was impossible to bring guns to bear in a turn. As an alternative, deflection-shooting in head-on or beam attacks improved somewhat with the introduction of optical, reflector sights. These were better than the existing ring and bead sights, but still left the pilot as the sole arbiter of the correct moment to open fire, a decision requiring much practice and fine judgement.