submarines

submarines. (See also anti-submarine weapons, midget submarines, sea power, and torpedoes.)

1. Design and development

Submarines during the Second World War only dived when necessary: most were designed primarily for good surface speed and endurance on diesels (see Table 1 for principal types). Submerged, typical storage batteries (recharged by diesels), powered electric motors for one hour at 8–9 knots or four days at 2 knots; but air became foul after about a day despite oxygen supplies and carbon dioxide absorption methods (French and German equipment was the best, followed by American, and later, British, equipment).

Submarines, Table 1: Some principal types

Country	Class	Dived Displacement (in tons)	Speed (Sur f/Sub)	Usual Armament	Remarks
Source: Contributor.
France	Rubis	925	12/9	2 TT(B)	Minelayer
	2 TT(S)
	1 TT in revolving tower amidships.
	32 mine-chutes
	76 mm A-A gun
Germany	Type VIIc	865	17/7.6	4 TT(B)	Atlantic. Guns from 1944 replaced
	1 TT(S)	by 1 37 mm (1.44 in) and
	88 mm (3.4 in) gun	2 x twin 20 mm A-A guns
	20 mm (.78 in) A-A gun
	Type IXD/42	1,804	19.2/6.9	4 TT(B)	U-cruiser: range 32,300 nautical
	2 TT(S)	miles 21 torpedoes,
	105 mm (4.1 in) gun 37 mm and	200 x 105 mm rounds carried
	20 mm A-A guns	Minelayer: range 21,000 nautical miles
	Type XB	2,177	17/16.4	2 TT(S)
	Mine chutes: 66 mines
	105 mm gun 37 mm and
	20 mm A-A guns
	Type XXIII	256	9.7/12.5	2 TT(B)	Coastal ‘Electro’
Italy	‘Calvi’	2,060	17.1/7.9	6 TT(B)	Atlantic
	2 TT(S)
	2 x 119 mm (4.6 in) guns,
	4 x 13.2 mm (.51 in)
	A-A guns
	‘Perla’	852	14.2/8.1	6 TT(B)	Med/Aegean
	99 mm (3.8 in) gun,
	4 x 13.2 mm A-A guns
Japan	RO-series K6	1,447	19.7/8	4 TT(B)	General purpose attack, range
	Light A-A guns	11,000 nautical miles
	B1 Type	2,584	23.5/8	6 TT(B)	Scouting. Carried 1 float
	I-15 series			140 mm (5.4 in) and	plane. Range 14,000 nautical
			A-A guns	miles
	Sto Type	6,560	18.7/6.5	8 TT(B)	3 float planes (bombs or
	1–400 series				torpedoes).
		Range 37,500 nautical miles
UK	‘S’	960–99	14.7/9	6 TT(B)	General purpose
	1 TT(S) in some 3 in or
	4 in (76 mm, or 102 mm)
	‘T’	1,571	15.2/8.7	8 TT B	Ocean-going.
	3 TT	Amidship tubes initially
	(5:2 amidships + 1 aft)	pointed forward.
	4 in (102 mm) gun, light	Welding increased range
	A-A weapons.	from 8,000 to 11,000 nautical miles by enabling certain ballast tanks to carry fuel.
	‘U’	730–5	11.7/9	4 TT(B)	Originally intended for
	(early boats 6)	training but proved ideal
	12 pdr or 3 in (76 mm) gun,	for Mediterranean
	light A-A weapons.	patrols.
USA	Fleet Gato-class	2,410–24	20.2/8.7	6 TT(B)	Habitability good for
	4 TT(S) 3 in	patrol endurance
	(76 mm) gun	75 days, range
		11,000 nautical miles
USSR	K-class	2,095	18/9	6 TT(B)	Long-range but not
	4 TT(S)	deployed far

The surface range of big submarines was many times that of a destroyer: and the bigger a boat the further and faster it could go—hence large American and Japanese submarines, for Pacific distances, and German ‘U-cruisers’. The Germans employed large Type 14 ‘Milch Cow’ submarines for refuelling and re-supplying smaller U-boats in the South Atlantic and Indian oceans.

By mid-1942 German U-boats could not safely surface at all, even at night, in areas covered by centimetric Allied airborne radar. A means of running diesels submerged therefore became essential and a Dutch invention, a Schnorchel pipe, which reached to the surface from periscope depth, was widely fitted in U-boats from early 1944.

Germany, then seeking optimum submerged performance in the face of new Allied anti-submarine measures, developed the streamlined Type 21 ‘Electro’ boat with a greatly increased battery capacity. Its top speed submerged was 17.2 knots and at 5 knots range was 365 nautical miles (667 km.) without using its Schnorchel except, briefly, to refresh the air. The six bow torpedo tubes could all be reloaded mechanically in five minutes against about 20 minutes per tube manually. Fortunately for the Allies, although the tiny sister ‘Electro’ Type 23 saw some coastal fighting, the powerful Type 21 came too late for active operations. Nor, in a radically different design tested in 1944, did the wholly air-independent ‘Walter’ turbine-propulsion system, supplied with oxygen and steam from the breakdown of hydrogen peroxide, become operational.

Meanwhile, the German workhorse was the Type 7c of 865 tons dived—a thoroughly good boat which underwent successive improvements to increase extreme diving depth to 300 m. (985 ft.) and range to 12,600 nautical miles (23,000 km.). Four bow tubes and one stern were sufficient for merchant ship targets.

Second after Germany in wartime evolution, but without a single-minded aim, Japan produced a number of remarkable submarines. Some carried bomber or reconnaissance aircraft—the huge 6,560-ton I-400 class could carry three aircraft—while others, normal attack types, could carry midget submarines or human torpedoes. Other boats were designed specifically to take supplies and reinforcements to besieged island garrisons.

There were some 30 Italian submarine classes; but, although impressive in peace—after the USSR, Italy had the world's largest submarine fleet—too many were ill-prepared for the rigours of war.

Among the Allies there were few noteworthy wartime developments. However, from 1942 British yards employed welding more widely (it was standard for German and American boats) instead of weaker riveting. Allied ancillary equipment—radar, ASDIC, fire control, communications—was steadily improved, with the US Navy making the speediest advances.

The Royal Navy was justifiably satisfied with its three principal classes—ocean-going T-boats; middling-sized versatile S-boats; and the handy little U-class (with the similar V-class) so suitable for Mediterranean work. None was innovative and none was fast; but all were dependable and well armed. The 3 in. (76 mm.) or, better, 4 in. (102 mm.) guns fitted on all classes were devastating against small vessels.

The American force consisted predominantly of excellent fast, long-range Fleet boats with four or six bow tubes, four stern tubes and quite good habitability for long periods at sea. Up to 32 mines could be embarked in reload torpedo stowages instead of 20–24 torpedoes. (Most submarines in all navies could substitute mines for torpedoes and carry a mix; but there were also purpose-built minelayers.)

Soviet designs ranged from the ‘baby’ 256-ton coastal M-class to formidable long-range 2,095-ton K-boats. Substantial numbers were available but they were not put to good use.

2. Warfare

Submarine strategy and tactics differed among the underwater belligerents; and objectives sometimes changed. The Samurai spirit of the Japanese demanded that their submarine arm operate against their opponents' warships; the clear aim of the Germans, on the other hand, was to destroy Allied merchant shipping, particularly those convoys around which the battle of the Atlantic raged; but submarines were also used, by both sides, as blockade runners and for delivering agents on to the opposing side's shores (see spies).

Just as in the First World War, U-boats nearly brought the UK to its knees. In 68 months about 2,000 Allied merchant ships, amounting to some 14.5 million tons, were sent to the bottom (see also UK, 9). Against that, 781 U-boats were lost—66% of the 1,170 commissioned, nearly 80% of the (approximate) 1,000 that actually operated. (Figures in this entry do not take account of midget submarines.)

At the outset, Hitler insisted on prize regulations being observed, though this did not prevent the sinking of the Athenia. Ordinary merchantmen were to be stopped and searched before being sunk; and the safety of crews had to be ensured. But the danger to U-boats from merchant ships which were armed, which attempted to ram, or which reported their position by radio, to say nothing of naval escorts, was plain, and the restrictions were lifted step by step. By August 1940 virtually no holds were barred. Then, after the Laconia affair in 1942, Dönitz directed that all efforts to rescue survivors were to cease: ‘Be severe.’

During their heyday (from 1940 to the end of 1942) U-boats were directed from shore HQ, in surface Wolfpacks, against convoys whenever possible. The exchange rate of ships destroyed to U-boats lost was then profitable at 14:1; but, when Allied anti-submarine measures began to take full effect, and when it became difficult for submarines to surface, it became unacceptably low—about 2:1 for the full year of 1943. Thereafter, U-boats continued to achieve isolated sinkings in all theatres but there was no longer any hope, despite new devices like the Schnorchel, of breaking the supply chain from the USA.

In 1939 British submarines had Axis warships, including U-boats, as priority targets. They were generally disposed along lines of individual patrol areas where, instead of chasing their prey, they waited, submerged, for it to come within range. However later, in the Aegean, the eastern part of the Mediterranean, and in South-East Asia, they were often given roaming commissions, to attack anything found, together with covert tasks such as landing agents. The ‘U’-class 10th Flotilla, operating under extreme difficulty from Malta during the siege of the island, demonstrated the effect of submarine warfare on a land battle. The havoc wreaked on Afrika Korps supply lines during the Western Desert campaigns caused Lt-General Fritz Bayerlein, Rommel's chief of staff, to admit: ‘We should have taken Alexandria and reached the Suez canal if it had not been for the work of your submarines.’

In all theatres, British submarines sank 169 warships (35 U-boats among them) and 493 merchant vessels, but 74 were themselves sunk—33% of those available.

The US Navy's submarine force in the Pacific war was hampered until mid-1943 by defective torpedoes; but subsequently its performance was magnificent. Like the UK, Japan was dependent on its merchant fleet as imports were essential, both for the economy and the war industry, while a very substantial outward flow of troops, arms, ammunition, aircraft, and food was needed to capture and hold Pacific island territories. Thus, in December 1941, the USA resolved, despite earlier protestations, on unrestricted submarine warfare against Japan's merchant marine. This strategy demanded different tactics; and peacetime caution was abandoned by fresh, spirited commanding officers who discounted the dangers of attacking on the surface or at periscope depth. Radar and sophisticated fire-control methods came to be employed with great success while ULTRA intelligence enabled USN submarines, using their high surface speed, to intercept their targets. Submarine warfare, amounting from mid-1944 to blockade, arguably spelled the end of Japan's fighting ability. Nearly 1,300 Japanese merchant ships, as well as one battleship, eight aircraft carriers, and eleven cruisers were sunk for the loss of 52 US submarines—18% of 288 in the force.

The Japanese Navy started the war with 60 submarines and continually added widely assorted types including boats which carried aircraft. Despite superb oxygen-fuelled torpedoes their score was relatively small because the attack boats were frequently sent, as part of the battle fleet, against heavily defended naval units instead of the more vulnerable American lines of communication. However, although fewer than a score of US naval warships were sunk by Japanese submarines, more than 170 merchant ‘supply’ and transport ships were lost to them. Japanese submarine losses amounted to 128 or 64% of the 200 available, but many of these were not engaged in combat operations.

When Italy entered the war in June 1940 it had 113 submarines which, after the USSR, was the world's largest submarine fleet. At the time its submarine equipment was thought to be modern and only 32 boats had been built before 1932. They were Mussolini's great pride, but the clarity of the waters they operated in—an aircraft could spot a submarine down to a depth of 40 m. (110 ft.)—the efficiency of British anti-submarine defences, and the immediate grip the Royal Navy imposed led, despite much activity, to poor results at the start of the battle for the Mediterranean (see Table 2). Total sinkings by Italian submarines during the war amounted to six warships and half a million tons of merchant shipping for the loss of 86 of their number, or 57% of the 150 which became operational.

Submarines Table 2: Italian submarine activity, June-October 1940

Month	Submarines employed	No. of actions	Naval tonnage sunk (t.)	Merchant tonnage sunk (GRT)	Submarines lost	Submarines damaged
Source: La marina italiana, xiii. 60, 73, 82, 92–3, 102. Maier, K. A., et al, Germany and the Second World War, Vol. 2 (Oxford, 1991).
June	97	105	4,180	9,920	6	12
July	59	65	1,350	5,141	none	4
Aug	36	42	uncertain	uncertain	1	none
Sept	27	32	none	none	1	1
Oct	27	37	1,475	none	5	none

The Soviet submarine fleet was strong numerically, but weak tactically. Exact numbers are not known (nor losses) but 75 may have operated in the Baltic—where one sunk the Wilhelm Gustloff—50 in the Arctic, and 50 in the Black Sea. Grossly inhibited by political over-control, robbed of good officers by Stalin's 1937 purge, often used purely for defence, and lacking proper fire-control procedures or reliable torpedoes, they made little impact on the German–Soviet war. According to one source ( S. Breyer, Guide to the Soviet Navy, 2nd edn., Cambridge, 1977) their losses were as high as the losses they inflicted, and sometimes higher. In the Baltic one submarine was lost for each ship sunk (51 each); in the Arctic they sank 45 ships but lost 25 of their number; while in the Black Sea 34 submarines were destroyed for the loss of 32 ships.

Among other Allied submarine services, the Dutch were exceptionally efficient, making a notable contribution in the Mediterranean and Far East; the Polish submariners, especially the crews of Sokol and Dzik, were experts; but of the seven French boats that escaped the German occupation to work on behalf of Free French forces, only the Rubis gained distinction—for a record-breaking 38 minelaying operations (683 mines) which claimed 21 victims.

Richard Compton-Hall

Bibliography

Alden, J. , The Fleet Submarine in the US Navy (Annapolis, Md., 1979).
Blair, C. , Silent Victory—The US Submarine War against Japan (New York, 1975).
Compton-Hall, R. , The Underwater War 1939–1945 (Poole, Dorset, 1982).
Friedman, N. , Submarine Design and Development (London, 1984), chs. 1–4.
Polmar, N., and and Carpenter, D. , Submarines of the Imperial Japanese Navy 1904–1945 (London, 1986).
Terraine, J. , Business in Great Waters—The U-Boat Wars 1916–1945, Part III (London, 1989).