Ocean Areas




THE GREAT CAPABILITIES of the submarine as a weapon of war were first revealed during World War I when the U-boat campaign almost proved decisive. Fortunately, the Germans themselves did not fully realize in 1914 how valuable the U-boat's ability to submerge and escape detection would be for offensive operations against enemy shipping. The small number of U-boats available to the Germans were used at first only to attack naval ships and it was not until 1915 that a concentrated attack was begun on English merchant shipping.

During 1915 and 1916 there were on the average only about 15 U-boats at sea at any time. These U-boats were sinking about 200,000 gross tons of shipping a month, while about 11/2 U-boats were being sunk each month. This situation was extremely satisfactory to the Germans, as the average life of a U-boat at sea during this period was about 10 months, during which the U-boat would sink about 13,000 gross tons of shipping a month, for a total of 130,000 gross tons of shipping sunk before the U-boat itself was sunk.

Encouraged by these successes, the Germans in February 1917 started a large scale campaign of unrestricted warfare on merchant shipping in an attempt to blockade England. This attempt almost proved successful as Allied shipping losses rose steadily to a peak in April 1917. Four hundred and forty-four ships of about 900,000 gross tons were sunk by U-boats during that month. The British Fleet was confined to its bases for there was only 8 weeks' supply of fuel oil in England. Various countermeasures had been tried without success and defeat seemed just around the corner unless an antidote to the U-boat could be found.


Admiral Jellicoe was brought to Admiralty to deal with the situation. The convoy system, twice turned down on account of lack of escort vessels and loss of time to shipping, was introduced in April 1917 and proved immediately successful in reducing the shipping loss rate. The result of all the various British countermeasures, of which the convoy system was the most effective, was that by October 1917, 1501 ships in 99 convoys had been brought into port with the loss of only ten ships sunk while in convoy (a loss rate of less than 1 per cent).


Although shipping losses had been checked, it should be kept in mind that, from an offensive point of view (i.e. destruction of U-boats), the U-boat had not been definitely beaten in World War I. After the start of unrestricted U-boat warfare in early 1917, the Germans maintained an average of about 40 U-boat at sea at any time. During this period the average number of U-boats being sunk each month was only about seven; the maximum number of U-boats sunk in any month was only 14 in May 1918. Therefore, the average life of a U-boat at sea during the last year of World War I was still about 6 months. Shipping losses, even during the last year of World War I, were still running at the level of about 300,000 gross tons a month, so that at that time each U-boat was still sinking about 45,000 gross tons before it, itself, was sunk.

These figures indicate that other factors besides U-boat losses must have contributed to the mutiny of U-boat crews in 1918, as the rate of U-boat losses had reached far higher levels in World War II without any corresponding crack-up in morale. Another point to be considered is that a larger part of German U-boat losses in the later part of World War I was due to mines, whose effectiveness was greatly increased by the fact that the geographical position of the German U-boat bases necessitated passage through the North Sea. Of the 178 U-boats sunk during the first World War, about 45 per cent were sunk by surface craft, about half of these by depth charges and half by gunfire and ramming. About 30 per cent were sunk by mines, another 10 per cent were torpedoed by submarines, and the other 15 per cent by other causes. It is therefore clear that the Allies had not developed any offensive weapon during World War I which could deal so effectively with the U-boat at sea that further operations would not be profitable.


That the Germans themselves still thought the U-boat was an effective weapon at the end of World War I may be seen from the fact that there were about 220 U-boat under construction in November 1918. Admiral Scheer's building program of October 1, 1918 provided for at least 30 U-boats a month beginning in the middle of 1919 and would probably have been fulfilled if hostilities had continued. If the war had not ended in November 1918 the Allies would have had to face a second and more intensive U-boat campaign.


One of the most significant points about antisubmarine warfare which became apparent early in World War I was the necessity of having scientific and technical aid in combating the U-boat. The essential problem was that of having some means of detecting a submerged U-boat and then having some weapon that would provide a good chance of destroying the U-boat.

The first crude attempt to develop an instrument to detect the submerged U-boat resulted in the installations of hydrophones on Allied naval ships in 1915. The hydrophone was simply an instrument for listening to the noise produced by the submarine, and sonic frequencies below 10 kc were used. No range and only a rough bearing were obtained from these early hydrophones and it was impossible to make attacks on U-boats with any degree of precision. The main effect of hydrophones was on U-boat morale, as U-boats found they were being followed after diving instead of being free of their pursuers.

The first depth charges to be used in attacking submerged U-boats were also introduced in 1915. However, so few were available that the Germans did not realize they were being used until 1917.

In September 1918 the British formed a small committee, consisting largely of scientists, called the Anti-Submarine Division International Committee (the initials spell ASDIC, the name given by the British to their echo-ranging detector). This committee developed a method of transmitting sound of supersonic frequencies under water and then using the echo returning from the submerged submarine to fix its position. Although the Asdic was still in the experimental stage when World War I ended, the labors of the committee were not wasted, as effective underwater echo-ranging gear was developed in the 1930s and proved to be quite a surprise to the Germans at the start of World War II. Due to the ability of Asdic to provide both range and bearing, it proved far better than the hydrophones used in World War I. Hydrophones, themselves, were improved by using supersonic frequencies and making them directional, thereby enabling the operator to obtain more accurate bearing.


At the start of World War II, England had only about 220 Asdic-fitted antisubmarine craft consisting of approximately 165 destroyers, 35 patrol craft (i.e., sloops, frigates, corvettes) and 20 trawlers. This total may be compared with the more than 3000 ships (about 450 destroyers, 170 patrol craft and the remainder trawlers and small craft) available to the Allies for antisubmarine warfare in 1918.

The British, profiting from their experience in World War I, had learned that the ocean convoy system did more than anything else to reduce shipping losses. They knew that the convoy system works best in open waters where evasion can be employed and that its success depends upon efficient escorts armed with effective offensive weapons. They were also aware of the fact that an efficient U-boat tracking system is necessary to practice effective evasion, and a daily U-boat plot based on contacts, DF fixes, and intelligence was used throughout the war.

Meanwhile the Germans had done considerable research in developing and improving U-boats. The U-boats available to the Germans at the start of World War II were faster than those used in World War I and were also considerably stronger, being able to dive deeper and to withstand more depth charge punishment. The Germans had also developed an electric torpedo which left no visible wake.

However, in September 1939, the Germans seem to have had available only about 60 U-boats, of which 30 were of the small 250-ton type (of limited endurance-suitable for coastal operations only) and 30 of the larger ocean-going type, 20 of which were of 500 tons and 10 of 750 tons. This small number suggests that Germany, possibly not anticipating that England would enter the war at that early date, had given higher priorities to the building of tanks and aircraft for land warfare than to the building of U-boats.


Chapter   Page
1 First Period--Submerged Daylight Attacks on Independents, September 1939--June 1940 3
2 Second Period--Night Surfaced Attacks on Convoys, July 1940--March 1941 8
3 Third Period--Start of Wolf Packs; End-to-end Escort of Convoys, April 1941--December 1941 16
4 Fourth Period--Heavy Sinkings on East Coast of United States, January 1942--September 1942 25
5 Fifth Period--Large Wolf Packs Battle North Atlantic Convoys, October 1942--June 1943 34
6 Sixth Period--Aircraft Defeat U-Boats' Attempted Comeback and Force Adoption of Maximum Submergence, July 1943--May 1944 44
7 Seventh Period--Schnorchel U-boats Operate in British Home Waters, June 1944--End of War 64
8 Summary of Antisubmarine Warfare, World War II 80

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Transcribed and formatted for HTML by Rick Pitz for the HyperWar Foundation