Anti-Submarine Measures from World War I

Author

A.N. Other and NHSA Webmaster

Subjects

Ship design and development, Naval technology, History - WW1

Tags

anti-submarine

RAN Ships

None noted.

Publication

June 2005 edition of the Naval Historical Review (all rights reserved)

Abridged from an article in “History of the World Wars”, previously published in the RAN Corvettes Association Newsletter Vol. 1 Issue 98 and kindly permitted to be reprinted here.

AT THE OUTBREAK OF WWI in 1914 the only weapons against the submarine were the gun or to ram. However both these methods depended on the submarine surfacing or giving away her position, and so opportunities were limited. In all, only fourteen U-boats were sunk by ramming and in many cases the attacking ship also suffered considerable damage. There were two passive methods of defense, minefields and nets, and these were quickly put into effect by both sides. First came indicator nets and then mine nets, which had small charges attached to the netting to explode on contact. Although the British took some time to develop a properly effective mine, when they finally introduced the H2 pattern in 1916 it rapidly became the most effective weapon against the U-boat, sinking 25 per cent of the total.

The depth charge was also introduced in 1916 to solve the problem of attacking a submerged submarine; it was basically a 300lb bomb fitted with a hydrostatic device to detonate it at a pre-set depth. Then came the need to devise a sensor to detect the submarine before it attacked, and from this were developed several types of hydrophone. This was simply an underwater listening device which was made directional to trace the noise made by the submarine’s electric motors. In July 1916 the motor boat Salmon brought off the first successful attack using both depth charges and hydrophones, when she sank UC7.

The simplest defense for a ship was to follow a zigzag course, because the U-boat’s commander had to estimate the target’s course and speed by eye. Any error in estimation of the speed or inclination of the target could result in the torpedo missing, and so ships were given false bow plates to disguise the bow wave and give a wrong impression of speed. This in turn led to ‘dazzle-painting’, a form of camouflage which utilised extreme colour variations and linear patterns to obscure features such as the waterline, deckline or bridge structures which helped the U-boat commander to estimate course and angle of inclination. Of course submarines also used camouflage to make them hard to pick out at a distance, and were reported to have hoisted sails on occasions to imitate fishing vessels.

Sweeps and Paravanes

Although the depth charge eventually proved to be the best weapon against a submerged U-boat there were a number of intermediate steps. The first was the explosive sweep, which was developed from minesweeping gear and comprised a charge towed from the stem of a destroyer, and kept below the surface by a special float. If the sweep fouled a submerged object this registered on an indicator and the sweep could then be fired electrically. Another device was the explosive paravane, two of which could be towed by a destroyer, in the hope that a submarine would draw the infernal device on to itself. Both these devices proved very unpopular with ship’s captains, who did not relish the idea of towing explosive charges with a habit of wrapping themselves around propeller shafts.

Depth charge throwers

A later development was the depth- charge thrower which could hurl an explosive charge some distance from the ship to the area in which the submarine had last been seen. There were several interim weapons. The 7.5 inch howitzer was simply a breech-loading recoilless weapon firing a spherical bomb. It was trained by means of a shoulder-piece and as it weighed only 35 cwt. it could be mounted in small ships like trawlers. It could fire its 100lb stick bomb a maximum of 2,100 yards, however its usefulness was limited because the bomb had no hydrostatic fuse to allow it to explode at a fixed depth. It was meant primarily for disabling a submarine on the surface or just after she had submerged. The 10-inch bomb-thrower was muzzle-loading and could fire either a normal shell or a spherical stick-bomb weighing 200lbs.

An even more fearsome weapon was the 11-inch breech-loading howitzer, which fired a 350lb shell some 3,000 yards; it could only be carried by cruisers and as it fired a conventional shell it was mainly for use against diving or surfaced submarines.

By far the most spectacular weapon against submarines was the decoy vessel or Q-Ship, simply a merchant ship with concealed armament, designed to lure a U-boat within gun range and then open fire. The first victims of the Q-Ships were quite easily trapped, but eventually some U-boats escaped and reported the news, and so a deadly game of bluff developed. The impression had to be one of an innocent steamer whose crew had taken to the boats, and so a ‘panic party’ had to leave the ship in the lifeboats, leaving the gun crew still concealed behind cover. If the U-boat commander was mildly suspicious he might indulge in some leisurely gunnery practice, and in some cases three ‘panic parties’ left before the lethal game could be resolved. As the U-boat always had the option of simply torpedoing the Q-Ship some of them were filled with timber to increase their chances of staying afloat, in the hope that the U-boat would then surface to finish her off with her deck gun. In 1917 a specially constructed Q-Ship was completed, HMS Hyderabad; she had one 4-inch gun, two 12 pounders, four bomb throwers, torpedoes and depth charges, all on a draught of just 6ft 9in so torpedoes would pass under her. Many of the ‘Flower Class’ escort sloops were either modified or completed as Flower-Qs, resembling small coasters, and some of the so-called P-Boats or patrol vessels were also converted. However they were warships, the armament concealed behind shutters under the deckhouses amidships and at the stern.

Decoy trick variation

A variation of the decoy trick was tried in 1915, when U-boats began to attack the British trawler fleet off the north-east coast of Scotland. In each group of trawlers was one naval trawler (commissioned but unarmed), which was towing an old ‘C’ Class submarine, to which she was connected by telephone. The theory was that when a U-boat attacked with her deck gun the trawler would give the position and range of the attacker to the submarine via the telephone link, the submarine would then slip the tow and work herself into a position for attacking the U-boat. The first time it was tried, in June 1915, the cable refused to slip, but despite the fact that the submarine C24 had 100 fathoms of tow rope and telephone cable dangling from her bows she managed to torpedo U-40. Nearly a month later C47 had another chance; this time the telephone link failed, but the submarine commander was able to work out what was happening on the surface and finally succeeded in torpedoing U-23.

However, the problem still remained of how to find submarines, and in April 1917 the shipping losses showed clearly that all countermeasures had failed. The fundamental problem was – and still is – that the ocean was far too big for the escorts to cover. The answer was the Convoy – merchant ships in groups defended by warships, the classical counter to harassment of seaborne commerce since the 14th century. But for a variety of reasons, 20th century naval tacticians could not accept that a method which had proved itself during the Napoleonic Wars could have any validity in the age of steam and armour. As late as January 1917 the Naval staff stated that convoys could not be recommended as a defence against submarines. There was no ‘inventor’ of the convoy in 1917, but much credit must go to influential advisers like the Secretary to the Cabinet, Hankey, who pressed it on Lloyd George, the British Prime Minister. The first change was in February 1917, when at French insistence, the cross Channel collier traffic was convoyed; within one month the collier losses dropped from 25 to 0.24 per cent. In the final analysis it was the convoys that forced the U-boats to take greater risks in trying to sink shipping. Convoyed ships totalled 84,000, of which the U-boats sank only 257, or 0.4 per cent. During a comparable period 2,616 ships were lost while sailing independently.

Net cutters

As the war progressed there was considerable development in counter measures by both sides. Very effective net cutters were soon devised; the Germans used a saw-backed frame and the British added a hardened edge to the bow.

Periscope design also improved from the early crude single instrument to the provision of separate search and attack periscopes. The search periscope had a wide-angle lens to allow the maximum field of vision, whereas the attack type had a narrow field. By the end of the war special air-search periscopes had been produced, with a high-angle head to allow a search for aircraft.

The biggest problem was the lack of endurance while running submerged, and there was a steady growth in battery capacity. The war showed that submarines could function in worse conditions than had ever been considered possible in peacetime. Conning towers were modified to allow greater protection to personnel, but the submarine proved to be more robust than many surface ships. Spray interference and lack of visibility were the limiting factors because of a submarine’s low silhouette, but really rough weather could be dodged simply by submerging, as the effect of waves does not go very deep.

The worst problems of habitability were the cramped quarters and the ever present condensation. One of the most grisly reports on conditions was sent in from a British submarine in the Sea of Marmara, where the crew were stricken by dysentery. Many of the problems could only be solved by increasing the size of submarines, and there was a clear link between the size of a boat and her efficiency on a long patrol. This was one of the main post-war improvements. Machinery improved dramatically and so did torpedoes, and by 1918 the submarine had gone through a revolution as rapid at that undergone by military aircraft in the same period.

The Russian ‘drop collar’

Some weird devices were quickly developed, one of which was an arrangement where the torpedoes were carried outside the hull and used a type of davit and sling which allowed the torpedo to be held at an angle or ‘pointed at the target’ before launching This device, called a drop collar, was developed by the Russians but was liable to damage from seaweed and flotsam, and the angling mechanism proved uncertain in its operation.

British K Class submarines

The British K Class submarines were 338ft overall, displaced 2,650 tons, had 10,000 hp steam turbines and a surfaced speed of 24 knots. They had two oil-fired boilers, each with a small funnel that had to fold down into a watertight well, also large air intakes which required watertight seals. With an auxiliary diesel for charging the batteries in addition to the electric motors there would have been absolutely no rest for the stokers on these submarines.

The first German minelaying submarine, carrying twelve mines, appeared in 1915. The mines were attached to a frame which had four legs that opened out when the mine was released through a hatch in the keel. The frame and mine sank to the sea bed with the frame and legs then forming an anchor for the mine. A soluble plug actuated a mechanism that released the mine on a length of cable and allowed it to float at the desired depth. This was an ingenious system but the soluble plugs proved unreliable; some dissolved almost immediately, releasing the mine under the submarine.

When we look at the early quaint examples one can only wonder how men could dare to put to sea in them. Surely submariners have always had a special brand of nerve to enable them to master their strange element – it called for the highest type of bravery and yet waged the most ruthless form of warfare at sea.