Anti submarine warfare

Anti submarine warfare

German submarines - U-boats - had devastated British merchant shipping from 1940 to the end of 1942. By 1943, anti-submarine warfare had become more sophisticated and the tide against the U-boats turned very much in favour of the Allies and by 1944, the Battle of the Atlantic had been won and the U-boats defeated.

Science played a major part in the battle to defeat the U-boats. Some anti-submarine devices had their seeds sown during World War One. However, major developments in sonar, ASDIC, depth charges etc occurred in World War Two along with new inventions against which the submarine, when on the surface or near the surface, had no defence.

The U-boat was highly effective when it could not be seen. When one or a wolf-pack attacked a convoy at night in the early days of the war, the night and the ensuing panic in an attacked convoy ensured their 'invisibility'. Hence the 2.6 million tons of merchant shipping lost to U-boats in 1940 alone. 

Improvements in sonar took aware this cloak of invisibility - even at night. Fitted onto a better developed type of warship - the frigate - by 1943, the U-boat became the hunted as opposed to the hunter. Frigates along with corvettes were relatively small warships but fast and heavily armed with depth charges. By acting as a convoy's 'bodyguards', frigates were a deterrent in themselves. They had been about pre-1939, but the pre-war versions were too small for Atlantic duty. The war versions were larger and could cope with the weather they were likely to experience at sea. HMS Towey was the first frigate of the River class - a warship specifically designed for ocean duty and the conditions the Atlantic would throw at it. HMS Towey displaced 1,370 tons ands had a maximum speed of 20 knots. Its armaments were 2 x 4 inch guns and ten 20mm anti-aircraft guns. Ships known as escort sloops were also considered to be highly effective in escorting convoys. HMS Starling was an escort sloop with a maximum speed of 20 knots, she displaced 1,350 tons and was armed with 6 x 4 inch guns and 12 x 20mm guns.

By criss-crossing a convoy, the ASDIC's on the protection ships could accurately pin-point the position of a U-boat by cross-referencing each fix. Modern sonar could give accurate distance and depth. By 1943, ASDIC was also more capable of differentiating between a U-boat and a large school of fish or whales. Once frigates and corvettes had locked on to a U-boat, they had the speed to catch it. All a slower submerged U-boat could do was to dive deeper. However, a U-boat captain knew that his submarine could only dive so far down before the pressure would take its toll on the hull of his submarine. 

A crude version of ASDIC had been used in World War One. By 1943, scientists, as would be expected, had developed a far more accurate version. The original ASDIC's had sent out just one sound impulse. If this hit something, a receiver would pick up the returned 'ping'. The amount of time between the outgoing impulse and the return ping gave an indication of how far away a U-boat was. The modern version used with great success in the later stages of the Battle of the Atlantic sent out three impulses at a time. Any return signal would show the distance away the U-boat was and the depth it was at in the water. With this information, frigates could start a combined attack. However, the modern version of ASDIC did have two weakness, one of which was of great value to a skilled U-boat captain. Depth charges were dropped off the back of a frigate. Therefore, as a frigate passed over the position where the U-boat was, it lost the signal and the U-boat to all intents disappeared. To counter this, a frigate sent out a spread of depth charges that covered where the U-boat was expected to be. A later development that solved the whole problem was the 'Hedgehog' and 'Squid'. The 'Hedgehog' was fired from the front of the ship - 24 smaller depth charges that were set to explode at different depths and at different times and to straddle the U-boats position. The 'Squid' fired just three charges from the front of the ship but they were larger than the 24 charges of the 'Hedgehog' and could crack the hull of a U-boat. Even if they missed their target, the explosive power of the three charges was such that many U-boats were forced to the surface. 

Even miles from a convoy, a U-boat' was not safe. All German submarines had to surface at some time to allow for a recharge of their batteries that could not be done under water. On the surface they were highly vulnerable. In the early days of the war this was less of an issue as in the so-called 'Black Gap' in the mid-Atlantic was out of the reach of Allied planes. However, by 1943, this gap had been plugged. Attack from the air became a major problem for U-boats - see photo above. The Short Sunderland, B-24 Liberator, Lockheed Hudson, Catalina and Wellington's were all potent forces against the U-boats. 

  Max Speed Max range Armament
Wellington 265 mph 3,200 miles 4 x .303 machine guns
6,000 lbs bomb
Lockheed Hudson 292 mph 2,160 miles 7 x .303 machine guns
4 x 500lb depth charges
Catalina 185 mph 3,750 miles 6 x .303 machine guns
4 depth charges
Short Sunderland 212 mph 2,980 miles  2 x .5 inch machine guns
12 x .303 machine guns
Max 2000lb of bombs/depth charges
B-24 Liberator 300 mph 2,100 miles 14 x .5 inch machine guns
5000 lbs of bombs internally
12,800 lbs of bombs externally





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