Search: Sort by:



Canadian sailors operating ASDIC, an early form of SONAR -Photo by William H. Pugsley- National Archives of Canada- PA-139273.

ASDIC (also known as SONAR) was a central feature of the Battle of the Atlantic. One crucial development was the integration of ASDIC with a plotting table and weapons (depth charges and later Hedgehog) to make an anti-submarine warfare system.

ASDIC produced an accurate range and bearing to the target, but could be fooled by thermoclines, currents or eddies, and schools of fish, so it needed experienced operators to be effective. ASDIC was effective only at low speeds. Above 15 knots (28 km/h) or so, the noise of the ship going through the water drowned out the echoes.

The early wartime Royal Navy procedure was to sweep the ASDIC in an arc from one side of the escort's course to the other, stopping the transducer every few degrees to send out a signal. Several ships searching together would be used in a line, 1–1.5 mi (1.6–2.4 km) apart. If an echo was detected, and if the operator identified it as a submarine, the escort would be pointed towards the target and would close at a moderate speed; the submarine's range and bearing would be plotted over time to determine course and speed as the attacker closed to within 1,000 yards (910 m).

Once it was decided to attack, the escort would increase speed, using the target's course and speed data to adjust her own course. The intention was to pass over the submarine, rolling depth charges from chutes at the stern at even intervals, while throwers fired further charges some 40 yd (37 m) to either side. The intention was to lay a 'pattern' like an elongated diamond, hopefully with the submarine somewhere inside it. To effectively disable a submarine, a depth charge had to explode within about 20 ft (6.1 m). Since early ASDIC equipment was poor at determining depth, it was usual to vary the depth settings on part of the pattern.

There were disadvantages to the early versions of this system. Exercises in anti-submarine warfare had been restricted to one or two destroyers hunting a single submarine whose starting position was known, and working in daylight and calm weather. U-boats could dive far deeper than British or American submarines (over 700 feet (210 m)), well below the 350-foot (110 m) maximum depth charge setting of British depth charges. More importantly, early ASDIC sets could not look directly down, so the operator lost contact on the U-boat during the final stages of the attack, a time when the submarine would certainly be manoeuvring rapidly. The explosion of a depth charge also disturbed the water, so ASDIC contact was very difficult to regain if the first attack had failed. It enabled the U-boat to change position with impunity.

The belief ASDIC had solved the submarine problem, the acute budgetary pressures of the Great Depression, and the pressing demands for many other types of rearmament meant little was spent on anti-submarine ships or weapons. Most British naval spending, and many of the best officers, went into the battlefleet. Critically, the British expected, as in the First World War, German submarines would be coastal craft and only threaten harbour approaches. As a result, the Royal Navy entered the Second World War in 1939 without enough long-range escorts to protect ocean-going shipping, and there were no officers with experience of long-range anti-submarine warfare. The situation in Royal Air Force Coastal Command was even more dire: patrol aircraft lacked the range to cover the North Atlantic and could typically only machine-gun the spot where they saw a submarine dive.




Copyright 2007/2019