The submarine was a subversive force. Its ability to hide within the element on which the battlefleet held sway threatened the great ships, the theory and practice of their employment, above all the admirals who had risen in their service; during the 1920s and 1930s these held power and patronage, not simply in the Royal Navy where, for reasons of proud historic supremacy and incipient decline, it might have been expected, but also in those younger, thrusting navies of the United States, Nazi Germany and Imperial Japan who looked to seize the trident. All these in the years leading to the Second World War cleaved to orthodoxy.

The articles of faith had been set down from 1890 by an American naval officer, Alfred Thayer Mahan, in a series of works extracting the principles of sea power from history – actually a period of history practically confined to the centuries of British naval ascendancy. Mahan placed the battlefleet at the core of naval strategy. By defeating the enemy battlefleet or bottling it up in port, the dominant fleet established ‘command’ of the oceans; and by blockading, that is throwing a cordon around the enemy’s coast, strangled his trade and brought him low. At the opposite pole to this strategy, and generally practised by the weaker naval power, was commerce-raiding, known after its French exponents as guerre de course. According to the doctrine this would never prevail over the superior battlefleet power.

The experience of the First World War appeared to confirm the theory. The British Grand Fleet had met the German High Seas Fleet off Jutland and driven it home, whence it had seldom ventured again, while the Royal Naval blockade had reduced the German population to near-starvation, anarchy and revolution. In the meantime, the German submarine or U-boat guerre de course had been contained.

Yet it had been a close-run thing. In April 1917 the British government had looked at defeat. That month, in which the United States entered the war against Germany, the Anglophile Admiral William Sims, despatched to liaise with the Admiralty in London, was horrified when shown the figures of merchant shipping losses: 536,000 tons sunk in February, 603,000 tons in March, 900,000 tons predicted for the current month. His dismay was heightened by a talk with the First Sea Lord, Sir John Jellicoe.

‘It is impossible for us to go on with the war if losses like this continue,’ Jellicoe told him.

‘It looks as though the Germans are winning the war,’ Sims replied.

‘They will win unless we can stop these losses – and stop them soon.’

When Sims questioned him about a solution, he said that at present they could see absolutely none.

Towards the end of the month Jellicoe, believing the government had not grasped the full gravity of the situation, wrote a memo to his civilian chief, the First Lord of the Admiralty, suggesting that it was necessary to bring home to the War Cabinet ‘the very serious nature of the naval position’:

We are carrying on the war … as if we had the absolute command of the sea, whereas we have not such command or anything approaching it. It is quite true that we are masters of the situation so far as surface ships are concerned, but it must be realised – and realised at once – that this will be quite useless if the enemy’s submarines paralyse, as they do now, our lines of communication.

He went on to suggest saving shipping space for the import of foodstuffs by withdrawing entirely from the Salonika campaign, and cutting down ruthlessly on all imports not essential to the life of the country,

but even with all this we shall be very hard put to it unless the United States help to the utmost of their ability … Without some such relief as I have indicated – and that given immediately – the Navy will fail in its responsibilities to the country and the country itself will suffer starvation.

This crisis in the naval war did not disprove the doctrine of battlefleet command since the Admiralty had brought it on itself by misunderstanding and thus disregarding the simplest, time-honoured response to guerre de course: convoying merchant ships instead of allowing them to sail independently while attempting to hunt the raiders. Mahan himself had written:

the result of the convoy system … warrants the inference that, when properly systematised and applied, it will have more success as a defensive measure than hunting for individual marauders – a process which, even when most thoroughly planned, still resembles looking for a needle in a haystack.

In desperation, and in response to more thoughtful officers in the fleet, at the eleventh hour the Admiralty introduced convoys for oceanic trade. Almost at once the shipping haemorrhage eased. It should have been a lesson: at the height of the campaign that April there were on average less than 50 of Germany’s 128 operational U-boats at sea at any time. It was this handful of comparatively inexpensive war machines which had come within an ace of sinking the most powerful naval and trading empire, aided not simply by her maritime allies, France, Italy, Japan and finally the United States, but also by the shipping and shipyards of neutrals. After the convoy system was instituted it was American yards building ships faster than the U-boats could sink them that allowed the Allies to transport sufficient materials and troops to win the Continental war.

In November 1918, as Germany’s acceptance of the armistice conditions became known, one of the U-boat COs, OLt. Karl Dönitz, who had been captured after his boat surfaced out of control while he was attacking a convoy, was held aboard a British cruiser off Gibraltar. He was watching scenes of jubilation in nearby ships with a bitter heart, when he found the cruiser’s captain approaching. Dönitz gestured at the ensigns flying from the armada of ships in the roads, British, American, French and Japanese, and asked the Britisher if he could take any pleasure from a victory attained with the whole world as allies.

‘Yes, it’s very curious,’ the Captain replied thoughtfully.’

A submarine was a thick-skinned steel cylinder tapering at both ends, designed to withstand enormous pressure at depth Buoyancy chambers termed main ballast tanks, fitted in most cases as lozenge-shaped bulges outside this pressure hull on either side, kept the cylinder just afloat. An outer steel ‘casing’ liberally pierced with openings to let the sea flood in and out provided a sharp bow, a faired stern and a narrow deck atop the cylinder; only a few feet above the sea, this was washed in any weather like a half-tide rock. About midway along its length rose a low structure enclosing another small pressure chamber called the conning tower, accessible from the pressure hull via a circular hatch and allowing access to the bridge above it by another small, pressure-tight hatch.

To submerge, the diesel engines which drove the craft on the surface, sucking air in through ducts from the tower structure, were shut down, and electric motors which took their power from massed batteries and consequently used no air were coupled to the propeller shafts. Buoyancy was destroyed by opening valves in the main ballast tanks, allowing the trapped air to be forced out by sea water rushing in; and horizontal fins, termed hydroplanes or just planes, projecting either side at bow and stern were angled against the water flow caused by the boat’s progress to impel the bows down. Approaching the required depth as shown on a gauge in the control room below the conning tower, the diving officer attempted to balance the boat in a state of neutral buoyancy, ‘catching a trim’ in which they neither descended further nor rose. He did this by adjusting the volume of water in auxiliary tanks at bow and stern, and either side at mid-length, flooding or pumping out, aiming to poise the submarine so perfectly that she swam on an even keel weighing precisely the same as the space of sea she occupied, completely at one with her element and floating firm and free as an airship in the air. It was an art attained by minute attention to the detail of prior consumption of stores and fuel, and by much experience. Sea water is seldom homogenous; a boat passing into a layer of different temperature or salinity, and hence density, becomes suddenly less or more buoyant, dropping fast or refusing to descend through the layer until more tank spaces have been flooded; when going deep the pressure hull would be so squeezed between the ribs by the weight above that it occupied less space and the boat had to be lightened by pumping out tanks to compensate. Most vigilance was required at the extremes: going very deep the boat might plunge below the point at which the hull could withstand the pressure; near the surface at periscope depth she might porpoise up to break surface in sight of the enemy.

Submerged, a submarine stole along at walking pace or less, either to conserve her batteries which could not be recharged by diesels until she surfaced again or, when hunted, to make as little engine and propeller noise as possible. With both sets of batteries ‘grouped up’ in parallel she might make twice a fast walking speed, 8 or 9 knots, but only for some two hours at most before the batteries ran dangerously low. This was her shortcoming: while she had great range and speed on the surface, once submerged she lost mobility by comparison even with the slowest tramp steamer. Against a battle squadron she could not hope to get within range for attack unless already lying in ambush very close to its track. For this reason the submarine was held to be ‘a weapon of position and surprise’.

Once her presence was detected and she became the hunted her submerged endurance was limited by the amount of air within the pressure hull, which of course was all the crew had to breathe; as they exhaled it became progressively degraded with carbon dioxide, after twenty-four hours or so reaching dangerous and finally fatal levels. Headaches and dizziness were common in operational submarines, but they were accepted among the other discomforts of an exacting life; remarkably little was known of the speed of deterioration of air. It was, for example, not appreciated that when the carbon dioxide content reaches 4 per cent thinking becomes difficult and decisions increasingly irrational; by 10 per cent extreme distress is felt, followed soon after by unconsciousness; at over 20 per cent the mixture is lethal.[7] No doubt this was not realized, and air purifiers were not installed – although in the German service individual carbon dioxide filter masks with neck-straps were provided – since before the advent of radar a submarine could usually surface at night to renew her air while remaining invisible. That indeed was the usual operational routine: to lurk submerged on the lookout for targets by day, coming up after nightfall to recharge the batteries, refresh the air and perhaps cruise to another position.

The submarine’s main armament was provided by torpedoes, each a miniature submarine in itself with a fuel tank and motor driving contrarotating propellers, a depth mechanism actuating hydroplanes to maintain a set depth, and a gyro compass linked to a rudder to maintain a set course. At the forward end a warhead of high explosive was detonated by a mechanism firing on contact or when disturbed by the magnetic field of the target ship. These auto-piloted cylinders, known as fish or in the German service as eels, were housed in tubes projecting forward from the fore end of the pressure hull and often aft from the after end as well. In some classes two or more tubes were housed externally beneath the casing, but unlike the internal tubes from the pressure hull whose reloads were stowed in the fore and after compartments, external tubes could not be reloaded until return to base.

While devastating when they hit the soft underpart of a ship or exploded beneath her, torpedoes were neither as accurate as shells from guns, nor for several reasons could they be ‘spotted’ on to the target. They were launched from their tubes – after these had been opened to the sea – set to steer a collision course to a point ahead of the target ship, ideally at or near a right angle to her track. Whether they hit depended largely on whether the relative motion problem had been solved correctly, which before radar meant how accurately the target’s course and speed had been estimated. The most certain data available was the target’s bearing read from a graduated ring around the periscope. Range was obtained by reading the angle between the waterline and the masthead or bridge of the target, either from simple graduations of minutes of arc or by a split-image rangefinder built into the periscope optics. Using the height of the mast or whatever feature had been taken, the angle was converted into range by a sliding scale. Since in most cases the masthead heights had to be estimated from the assumed size or class of the target ship, usually a difficult judgement to make from quick periscope observations, and since there was a tendency to overestimate size, ranges were often exaggerated. In addition the observer made an estimate of the angle between the target ship’s heading and his own line of sight, known as ‘the angle on the bow’; this too was often overestimated. Speed was deduced from a count of the propeller revolutions audible through the submarine’s listening apparatus, the distance of the second bow wave from the stem, or simply from the type of vessel and experience. With this data a plot was started incorporating both the target’s and the submarine’s own movements; updated by subsequent observations as the attack developed, the plot provided increasingly refined estimates which were fed into computing devices of greater or less mechanical ingenuity according to the nationality of the submarine. In British and Japanese navies the firing solution was expressed as an aim-off or director angle (DA) ahead of the target, in the US and German navies as a torpedo-course setting. Finally, a salvo of two or usually more torpedoes was fired with an interval of several seconds between each; this was to avoid upsetting the trim with such a sudden release of weight as would result from the simultaneous discharge of all tubes, and to allow for errors in the estimated data or the steering of the torpedoes themselves. In the British service, where it was assumed that at least three hits would be required to sink a modern capital ship, COs were trained to fire a ‘massed salvo’ of all torpedoes – usually six – at 5-second intervals, so spreading the salvo along the target and its track. In the American and German services particularly, where the torpedoes themselves could be set to run the desired course, ‘spread’ was often achieved by firing a ‘fan’ with a small angle between each torpedo.

Few attacks were as straightforward as this description might imply: the target was generally steering a zigzag pattern; surface and air escorts were often present to force the submarine into evasive alterations during the approach. The periscope could be used only sparingly, the more so the calmer the sea, lest the feather of its wake were spotted by lookouts; and between observations the submarine CO had to retain a mental picture of the developing situation, continuously updating calculations of time, speed and distance in his head as he attempted to manoeuvre into position to catch the DA at the optimum time when the torpedoes would run in on a broad angle to the enemy’s track. There were other situations when snap judgements had to be made on a single observation or while the submarine was turning with nothing but the CO’s experience and and eye to guide him. It was sometimes said that a successful CO needed a sportsman’s eye. Like most generalizations about submarine COs, this can be disproved by individual example: David Wanklyn, for instance, the highest-scoring British ace, did not shine at ball games.

Some British COs appear to have dispensed with overmuch calculation: John Stevens, the very successful CO of Unruffled in the Mediterranean, remarked, ‘I say if the target’s worth firing at, give him the lot [a full salvo] and, anyway, the DA is always ten degrees.’[8] It is not possible to compare the results of this cavalier approach statistically with those of American or German COs who relied on fire-control computers generating continuous solutions since the three services operated in very different conditions and, particularly with the Americans, the percentage of hits was depressed by torpedo failures. All that can be deduced from the figures is that all navies had a few COs who consistently outhit the average, and at the other end of the scale a few who seldom hit anything. The qualities the aces showed were aggression, determination, imperturbability in attack, and painstaking attention to training. To a greater extent than in any other type of warship, officers and crew were simple extensions of the CO’s will. When he attacked submerged, he alone saw the enemy – apart from some US submarines where the executive officer took the periscope – and it was the CO’s coolness, resolve and daring, or his timidity, exhaustion and nervous fatigue, that decided the course of the action.

The submarine, more than any other warship, was designed and operated as what would now be called a weapon system. Except in the US service, no concessions were made to the comfort or even the convenience of the crew. They were carried merely to serve the system, fitting in the spaces around the reload torpedoes and stores for the voyage, in most cases sharing bunks, ‘hot bunking’ with a shipmate from another watch and sleeping on unchanged sheets that became dirtier by the day. They were unable to bathe or shower, scarcely to wash hands and face, and frequently could not get dry after a wet spell on watch. There was often a queue for the fiendishly complex WC in the heads, and even that could not be used when submerged below about 70 feet because of the exterior pressure. Thereafter they were obliged to relieve themselves in buckets and empty bottles whose smell mixed with the confined, humid odour of diesel oil, past cooking, unwashed bodies, chlorine and stale bilges which permeated every area. They were forced to eat hashes of tinned food and dehydrated vegetables after the fresh provisions ran out, could not take proper exercise, could not even walk on the deck casing lest an enemy aircraft were sighted and the boat had to make an emergency dive; and when submerged for any length of time they were subject to nausea, splitting headaches and, if the mind were allowed to dwell on it, incipient claustrophobia. Paradoxically, the sheer frightfulness of conditions and the sense of vulnerability, and hence of mutual responsibility, engendered comradeship across barriers of rank which in turn ensured high morale, probably higher than in any other class of warship, irrespective of nationality. It depended, however, on a good CO; this meant above all an officer who, whatever his qualities or faults, the men felt they could trust.

It was a young man’s game. In the British service an officer was judged too old for operational command at 35. The US service began the war with COs for fleet submarines nearer 40 than 35 but many proved overcautious, which may have had more to do with unrealistic peacetime training than with age; they were soon replaced by younger officers whose aggression, helped by radar, was largely responsible for the devastating campaign which severed Japan from its external supplies. By the last year of the war most US submarine COs were in their early thirties, many not yet 30. In the German service a more dramatic decline in the age of COs was due to the loss of men in the Atlantic and the simultaneous expansion of the U-boat fleet; in the later years many German COs were under 25; youngest of all was Hans Hess, who was 21 when he took command of U995 in 1944.

Who in sound mind volunteered for the hazards of such an unnatural life? Before the war sufficient came forward in all navies, and it was only necessary to draft a few, mostly specialist ratings. Some would insist they joined for the extra allowance paid for service in submarines, or because they needed the extra money to get married. There were other powerful inducements: for officers, especially, responsibility and command came much earlier than in the surface fleet; for all hands there was the special camaraderie and informality of the close life aboard, and a different kind of discipline, maintained more by competence and self-respect than by mere rank. In a submarine more than in any other type of vessel each member of the crew was vital to the team; a mistake by any one person might lead to disaster. It was in every sense a close fraternity with all the certainties and reassurance of such, bonded by shared trials, miseries, unique hazards and proficiency in overcoming them. In every navy the submarine service was a club apart with a particular esprit de corps, attracting the bright and non-conformist seeking escape from the hierarchy and meaningless apple-polishing of a big-ship navy in peacetime. The future German aces, Prien, Schepke and Kretschmer, were of this type, as was the American submarine CO Ignatius Galantin, who wrote of his two years’ battleship service after graduating from the Naval Academy: ‘I became increasingly restive … I wanted to be free of the dull, repetitious, institutionalised life of the battleship navy, and to be part of a more personalised, more modern and flexible sea arm.’

As Galantin hints, the submarine was exciting as a new weapon at the forefront of naval technology and strategy. On the other hand it had retained from the first war the aura of clandestine, piratical operations by such COs as Martin Dunbar Nasmith, who had forced the nets, minefields and powerful currents of the Dardanelles to attack Turkish transports for Gallipoli in the Sea of Marmora; Max Horton, whose exploits in the Baltic had led the Germans to put a price on his head; and from the other camp Lothar von Arnauld de la Perière, ‘ace of aces’, whose record of ships and tonnage sunk remains unbeaten, and Dönitz’s first CO, Walter Forstmann, who stands only a little below Arnauld in the record book.

One of the distinguished band of British submariners (now Vice-Admiral Sir) Ian McGeoch has listed his reasons for volunteering:

I was a dedicated small boat sailor, and navigator in offshore racing yachts; I was keen to get the early command which submarine service offered; I was engaged to be married, so that the extra six shillings per diem was an attraction; and I had read most of the accounts of the operations of British submarines in WW1.

In both Germany and Japan, where youthful idealism was harnessed to a martial ethic, the submarine arms were deliberately raised to élites, their image enhanced by propaganda; in Germany posters depicted dashing U-boat heroes sailing under streaming pennants towards the enemy. Despite this, during the war both Germany and Japan, while attempting to maintain the fiction of an all-volunteer service, resorted increasingly to drafting suitable young men from the surface fleet, as indeed happened in Great Britain and America. But even when drafted, by no means all measured up to the physical and temperamental demands of submarine life. In all navies the submarine branch remained an élite of fit, stable young men from which temperamental misfits and those not prepared to pull their weight were very quickly weeded, or weeded themselves.

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