It is interesting to compare the genesis of Sonar, the U.S. Navy’s sound-ranging instrument for the detection of hostile submarines, with Asdic, the British instrument developed for the same purpose. In the December, 1945, issue of the British magazine Discovery, the starting point of both Sonar and Asdic is described by Lieutenant Commander S.J. Brookfield, R.N.V.R., who was Naval Assistant to the Deputy Controller (Research and Development) at the Admiralty during World War II. The basic principle on which these two instruments work first emerged from a disaster that horrified the public on both sides of the Atlantic thirty-five years ago! Lieutenant Commander Brookfield remarks:
It is interesting to note that the idea of pointing an echo-sounder forward to look for obstacles ahead was first suggested and patented in 1912; the proposal for such a device was directly inspired by the Titanic iceberg disaster. With the oscillator available at that time, the range obtainable was too short to be useful, and the patent was allowed to lapse.
Then came World War I, and the severity of the shipping losses led to an agreement between the Allied and Associated Powers that all their ideas in anti-submarine weapons should be pooled. Hence came the creation (in 1917) of the Anti-Submarine Detection Inventions Committee, and it is from the initial letters of these five words that we get A.S.D.I.C. So desperate was the situation then, that anything and everything in the way of new anti-submarine weapons had to be looked into, and thus it came about that the 1912 idea of sub-surface sound-ranging was taken up again. And with what results? Lieutenant Commander Brookfield says:
Allied experiments in 1917 showed little promise until it was suggested that the piezo-electric property of a quartz crystal might be used to produce a highly effective supersonic oscillator. With this innovation, the range leaped up. Twelve sets were ordered for installation in ships, but the war ended before they could be put into operation.
And, in a footnote, we get the following useful information:
The piezo-electric effect is a phenomenon, exhibited by certain crystals, of contracting along one axis and expanding along another when subjected to an electric field.
Here it may be as well to interject also the explanation that the part known as the “transducer” in the American Sonar is called the “oscillator” in the British Asdic. Bearing this, and the foregoing statement in mind, we are now able to appreciate more fully the comparison between the two types of instrument as described in a recent article on Sonar in the U. S. Naval Institute Proceedings:
The primary differences are: British Asdic transducers consisted of sandwich arrangements of quartz and steel, whereas U. S. Sonar transducers consisted of a battery of nickel tubes driving a steel plate by magneto-striction.
So it was away back in 1917-18 that the British Navy struck out along its own line of development by using the piezo method in its new anti-submarine apparatus.
The first type of Asdic was rather a crude affair, for Lieutenant Commander Brookfield tells us that the oscillator (transducer) “had to be suspended in the water by hanging it over the side of the ship. ...”
World War I stopped before sound-ranging could be brought into use against the Kaiser’s U-boats. After the 1918 Armistice, the twin sisters Sonar and Asdic were separated and grew up on each side of the Atlantic. The article in the Naval Institute Proceedings has told us how the Sonar equipment was developed between the two World Wars “by about twenty scientists working at the Naval Research Laboratory in Washington.” And what, during that same period, was the concurrent growth of the British Asdic device? Once again, Lieutenant Commander Brookfield has the story:
From then (1918) onwards, a keen team of naval scientists worked on the problem of submarine detection in the shore-based H.M.S. Osprey at Portland. They kept up their enthusiasm for the work despite the technical isolation from other scientists imposed on them by security requirements, and despite the flagging public interest in naval equipment in those days. Thanks to them our ships were fitted with Asdic sets when war came in 1939.
And, speaking elsewhere of the phase of development between the two wars, he says:
The Osprey team, although hampered by cuts in personnel and lack of money, developed the apparatus to a stage far in advance of any other nation, and many years ahead even of those Allies who had collaborated with us in the early development.
So it seems that Miss Asdic grew up a little faster than Sister Sonar!
When Coastal Command and the Royal Navy collected the U-570, the captured German submarine was re-christened H.M.S. Graph. If you asked why she was so named, you were simply told: “It’s Asdic’s job to produce a graph—and there’s one!” Here we encounter another of the primary differences between Asdic and Sonar. The Asdic ranges were permanently recorded on a range-recorder, whereas the Sonar ranges were indicated by a neon light flashing on a range-marked dial.
By text and illustrations Lieutenant Commander Brookfield shows how the British instrument converted acoustic detection into a graphic record. Quite naturally he also alludes to those extraordinary conditions of the most strigent secrecy under which Asdic was designed, developed, and produced across a period of twenty years:
Seldom has secrecy been maintained over so many years, and seldom has it paid Such good dividends as it did in this case. For some time the enemy thought that, as in the last war, we were relying on hydrophones to listen for the underwater sound from a submarine’s engines and he devoted much effort to reducing their noise. But our Asdic sets, of course, were just as effective however quiet the submarine became, and his early counter-measures were quite useless. At last he developed Pillenwerfer—large chemical balls for the submarine to eject, which produced streams of bubbles giving an Asdic reflection, in the hope that our operators would follow the decoy instead of the target.
However, Sonar and Asdic both had the same end in view—the downfall of the submarine. They worked together on the same principle of sound-pulse and echo so it may be truly said of them that they were “Two minds with but a single thought, two hearts that beat as one.”
The long contest between Submarine and Anti-Submarine is by no means over. On the contrary it has entered a new and even more intense phase. Marshal Foch said that “each new war begins where the last one ended.” So it came about that the Asdic equipment which arrived too late for use in 1918 administered the first sharp check to the U-boats in 1939. The next war—if there is one—will therefore begin where the last one ended. And how did World War II end?
When the Capitulation came, Anti-Submarine had gained the upper hand, but the Submarine was fighting back to regain its old mastery. The Germans were preparing to put into service new types of U-boats, built with new forms of pressure-hull, driven by new types of engines and batteries, firing new kinds of torpedoes and using a new technique of attack. It will be against craft of this kind, or even better, that the next contest will begin.
The submarine of the future, when engaged on war operations, will probably dive soon after leaving her base, and then cruise submerged for thousands of miles on end, using a “Schnorkel” breather tube to feed air to her diesels or gas turbines. Battery power—which now permits of underwater speeds of 16 knots and more—will be conserved for approach and attack. Sonar and Asdic cut both ways: if they can be used by surface ships to find submarines, then the submarines can use these same instruments to find surface vessels. No periscope may appear above the surface to betray the submarine’s approach. And if she fires a trackless torpedo, there will be no air-stripe to give a clue to her attacking position. A faulty approach and arrival at a bad firing point will not matter so much, because a torpedo that “homes” on to its target will compensate for errors made during the run-in.
You may say that Sonar and Asdic will give their warnings of approaching danger, and that the anti-submarine craft will begin their counter-attack before the submarine begins her attack. The reply is, you cannot count on that as a certainty. Lieutenant Commander Brookfield is quite impartial in his account, for he shows that the Asdic equipment was not an infallible method of anti-submarine detection. Under certain conditions of sea temperature, the searching sound-beam was curved down to the sea bed: under others, it developed a dangerous “dead spot” ahead of the searching vessel. Again, in inshore waters, submerged rocks and reefs may give back false and misleading echoes. The Germans found out that Radar and Asdic lost their efficiency against a land background, and so they quitted the midocean spaces and took to submarine operations in coastal waters. Thus the wheel turned full cycle, and at the end of World War II the coastal waters of Cornwall were infested by U-boats, as they had been at the end of World War I.
If the submarine of the future is detected before, during, or after her approach and attack, and is subjected to counter-measures, what can she do? She can do two things: she can dive deep, or she can run for it. New types of pressure-hull and all-welded construction allow a submarine to dive—where soundings permit—to a depth of a hundred fathoms and more, and by going deep she can find a far greater immunity from depth charges. If she elects to run for it, and can make a submerged speed of 24 knots, it stands to sense that she is not going to get overhauled by 18-knot DE’s, sloops, frigates, corvettes and the like. So it comes about that the doubling and trebling of the submerged speeds of submarines have made the great mass of anti-submarine craft built during the recent war into a pack of peg-legged police.
Sonar and Asdic may locate the submarine—but you have to catch your hare before you can cook it!
What is Anti-Submarine going to do about it?
There is one inexorable, inescapable fact:
No vessel, whether of the surface or submarine type, can hope to escape from aircraft attack by running away. Speed will not save her, because aircraft are, and always will be, faster than surface and sub-surface vessels. Therefore, no matter how much the submarine increases her speeds on the surface and beneath it, she will always be overtaken by aircraft. Anti-submarine warfare of the future may become even more an affair for aircraft than in the past.
The British Press has published a few illustrations of a U.S. anti-submarine magnetic locator. Shaped rather like a small aircraft bomb, it could be lowered into the sea at the end of a long cable and towed by a searching aircraft. Was it this device or the Sono Buoy which led to those rather agitated complaints in the German Press of 1944, to the effect that “the Allies now possess some occult device which enables their aircraft to find our submarines, even when the submarines are moving in a completely submerged condition”?
Of the Submarine of the Future, an account has been given above. Do we now get some dim vision of the Anti-Submarine Type that is to come? She may be a giant flying-boat, using Radar, Sonar-Asdic, Sono Buoys and magnetic locators. And having found and fixed her target, she may use some kind of jet-propelled depth charge, a sort of inverted V-2 weapon which will drive itself swiftly down into those greater ocean depths where the “bathysphere-hulled” submarine is trying to find safety from the wrath to come.
Will that be the end of it? Perhaps not! As one who has studied submarine warfare and anti-submarine weapons for over thirty years, perhaps I may be allowed to add this final word: Only when man equips himself with the power of long range submarine vision, will Anti-Submarine gain the final and decisive victory over its opponent. For once you have stripped the submarine of her power of secret sub-surface movement, she becomes naught but a coffin ship.
For many years editor of the famous naval annual Jane’s Fighting Ships, Mr. Prendergast began his journalistic career by writing articles for the British Navy League Journal at the age of 18. From 1936 to 1946 he contributed monthly articles to The*Navy (London). He was coauthor with R. H. Gibson of The German Submarine War, 1914-1918, published in the United States, France, and Spain as well as in England.