The Seesaw of Submarine Warfare

by JAMES PHINNEY BAXTER

1

THE side that loses a war usually writes the best history of it. The Germans, who knew that their submarines had brought them close to victory in 1917, produced far and away the best account of the U-boat war — Arno Spindler’s Der Handelskrieg mit U-Booten. They noted the lessons of the war, based sound tactical doctrine on them, and planned how to build more and better submarines and to man them better.

“I will show that the U-boat alone can win this war,” boasted Grand Admiral Doenitz in 1940. “Nothing is impossible to us.” He had almost every reason for confidence: more and better submarines than his predecessors had, and equally bold commanders. Had not Gunther Prien taken his U-boat into Scapa Flow itself on the night of October 13, 1939, and sunk the battleship Royal Oak?

When the war began, neither the Axis powers nor the Allies were prepared for intensive submarine warfare. The Germans had only about twenty 500ton and ten 750-ton ocean-going U-boats. In 1918 Great Britain alone had 400 destroyers, and her allies and associates brought the total close to 900. In 1939 the British went to war with only 180 destroyers. France had 59, but most of these were needed in the Mediterranean. The British had fitted their asdic (underwater sound gear) on 165 destroyers and 54 smaller craft.

The United States had about 60 destroyers fitted with echo-ranging gear and some of these were transferred to Great Britain in the exchange of bases for overage destroyers. The establishment of scientific interchange with Great Britain brought us information of much value concerning subsurface warfare. At the outset of the war, British antisubmarine craft carried no radar, no long-range aircraft were assigned to anti-submarine patrols, and the short-range aircraft carried 100-pound bombs quite unsuited to their task.

In the First World War the greatest advantage enjoyed by the British was their geographical position, which enabled them to block the exits from Germany to the Atlantic. Now General Geography had turned traitor. The conquest of Norway, Holland, Belgium, and France gave the Germans a broad ocean front of 2500 miles, with ports outflanking Great Britain from Bordeaux to Narvik. Operating from these longer coastlines, the U-boats steadily increased their kills. The Germans strove to launch a score or more submarines a month, and as their losses were very few, the number of U-boats at sea rose steadily. Shipping losses were 515,000 tons in March, 1941, 589,000 in April, 498,000 in May, 329,000 in June, when the nights were short. Then the British stopped publishing monthly figures. As the British improved their anti-submarine ordnance and the range of their patrol planes, the U-boats operated further west and began to attack on the surface by night, diving deep when hunted and varying their depth as a counter to the asdics.

During the winter the British introduced radar into their surface craft and patrol planes to spot U-boats on the surface. This move greatly increased the area covered by search and the number of sightings. When the U-boats began to attack convoys at night in groups, they made considerable use of radio to direct and assemble the “wolf packs.” This gave away their position to the high-frequency direction finder, or “Huff Duff.”

Aircraft of the Coastal Command, in the first two years of the war, escorted 4947 merchant convoys, made 587 attacks on U-boats, and flew some 55,000,000 miles. In May, 1941, they launched a vigorous offensive in the transit areas through the Bay of Biscay and north of Scotland. They did not get many kills, but they drove the U-boats under.

This fact alone was of great importance. When a submarine submerged, her speed dropped to 2 or 3 knots. She could, it is true, put on full submerged speed, say 6 or 7 knots, but if she kept it up she would exhaust her batteries in less than an hour.

Passage through the Bay of Biscay became a long and risky business.¹ The U-boat remained submerged by day, surfacing at night to recharge her batteries and to ventilate. On the surface, even though she maintained radio silence, she could be detected by radar. Except in its gravity, the submarine war was becoming more and more unlike that of 1917. At that time the U-boats worked as genuine “submarines,” diving by day and attacking submerged, surfacing at night. They were individualists with a free hand, working in the limited areas of coastal waters and the close approaches to the British Isles. In 1941, the U-boats were operating as submersibles, diving only when forced to do so, and attacking at night on the surface as torpedo boats. They reconnoitered and attacked in groups, under the orders of the Admiral on shore, who controlled all their activities from the moment they sailed until their return to port.

When the United States entered the war, the Germans found a happy hunting ground on our Eastern seaboard. By that time they had about 200 ocean-going submarines and were commissioning about 20 a month. The transatlantic convoys were often hard nuts to crack,² but our Navy was too short of anti-submarine craft, both surface and air, to start coastal convoys until May, 1942. The system was gradually extended to the Gulf of Mexico, the Caribbean, and the South American coast as vessels became available.

Since the coastal route was too long to cover adequately by patrol, the sinkings — especially of tankers and large ships — meanwhile reached catastrophic proportions. Some 6,250,000 gross tons of shipping — over 40 per cent of the total loss to submarines during the war — were destroyed in the year 1942. Twenty-five ships were sunk off the mouths of the Mississippi, twenty-five more off the Florida coast between Key West and Daytona Beach. Some of the German submarines were minelayers. These closed Chesapeake Bay to traffic for two days in June and three in September, and bottled up New York Harbor for three days — November 13 to 15, 1942.³

To beat the submarines and make the Atlantic safe for the ships carrying the troops and supplies needed to help breach Germany’s European fortress required prodigious efforts by Britain, Canada, and the United States. Huge programs of anti-submarine craft expanded the Royal Canadian Navy to close to 700 vessels and gave the United States 306 new destroyer escorts between April and December, 1943. In merchant shipbuilding all three nations performed miracles. American yards turned out the hitherto unimaginable total of a million tons a month.

To direct this vast effort required the utmost in organization and administrative skill, and the utmost was forthcoming. While the Bureau of Ships, the Maritime Commission, and American shipbuilders combined to set all-time records, Admiral King reorganized the Navy command, creating under his direct command in May, 1943, an extraordinary organization, the Tenth Fleet, with Rear Admiral Francis S. Low as its Chief of Staff.

“The Tenth,” says Admiral King, “was a fleet without a ship. However, this highly specialized command coördinated and directed our naval forces in the Battle of the Atlantic, making available the latest intelligence to the Commander in Chief, U. S. Atlantic Fleet, and to other fleet and sea frontier commanders who directed the actual operations at sea, and supplying anti-submarine training and operating procedures to our forces afloat. The Tenth Fleet correlated the anti-submarine developments of the various technical bureaus of the Navy Department and the fleet training schools concerned with anti-submarine activities. In addition, it worked closely with the General Staff of the United States Army and with the British Admiralty and Canadian Naval Headquarters to avoid duplication and confusion, and to insure that maximum effort would be directed against the German underseas fleet.”

When forced to cope with U-boats off our coast in 1942, our Navy was lamentably short of aircraft and surface vessels. The heavy requirements for troop convoys in the Atlantic and Pacific absorbed most of our available anti-submarine craft. We had turned over 50 old destroyers to the British in exchange for bases. To help us get coastal convoys started, the British allocated 24 trawlers and 10 corvettes, and recast the system of transatlantic convoys to release other patrol craft. Wherever convoys could be introduced, losses fell to modest proportions, as the U-boat promptly shifted to fields where the pickings were easier.

Though convoying was of great value, it was still not enough. Army and Navy aircraft, assisted by the Civil Air Patrol, did the best they could to cover our coastal waters, but at first their numbers were inadequate and their kills were few. Heavy bombers might pound the factories where U-boats were built and the dock areas in the ports where they refitted, but the Nazis covered their submarine pens with concrete slabs thick enough to stop block-busters. More ships and more planes of longer range were in part the answer, but both ships and planes needed new detection devices and new weapons.

2

AT SEA we seemed to be losing the war. During June, 1942, an average of 48 U-boats operating at sea sank 143 ships. Each U-boat was living long enough to sink 20 ships. They remained at sea for long periods, obtaining food, fuel, and torpedoes from “cow” or supply U-boats, each of which took care of about 10 U-boats.

So grave was the peril that some fanciful projects received respectful attention. Among them was the Habakkuk project, originated by the British in September, 1942, for an iceberg aircraft carrier of 2,000,000 tons, 2000 feet long, 300 feet wide, and 200 feet deep. This floating airfield, to serve as a base for anti-submarine patrol planes and to provide air cover for landings in Europe, was to carry planes and anti-aircraft guns and be propelled “at a few knots” by means of “a large number of electric engines attached as nacelles” to an outer insulated skin. Since ice proved too weak and brittle for the purpose, engineers devised a mixture containing wood pulp and dubbed it “pykrete.” The project, on which the Canadians had made some progress, was discussed at the Quebec Conference in August, 1943, but was dropped the following December.

Subsurface warfare went through an extraordinary transformation from 1941 to 1945. The United States Navy, like the British, started the war with well-developed echo-ranging gear, but its ordnance, since the depth charge was practically the same as that used in World War I, was obsolete against a submerged submarine of modern construction. Operations research, still in its infancy, had been limited to some study of peacetime maneuvers. Operating personnel and methods had not yet been tested in war. Training of specialists in operation and maintenance had been undertaken, but it was still far from satisfactory. Perhaps of even greater importance, definite knowledge as to the behavior of sound in the ocean was still lacking. Clearly the laws governing underwater sound required further study in order to formulate reliable operating procedures and to govern the design of sonar gear.

Fortunately our Navy had entered into a most effective and fruitful partnership with the National Defense Research Committee. It must be emphasized at once that the outcome was a Navy victory won with civilian help, and that considerable portions of the story must remain shrouded in secrecy.

It may well be that the greatest contribution made by scientists to subsurface warfare lay in the application of statistical analysis to the records of operations and in the development of doctrine. Tactics had to be improved for old gear and devised for new. Much of the new anti-submarine equipment was relatively unfamiliar to Naval officers, and in the feverish days of 1942 no headquarters staff had at its disposal an adequate number of persons sufficiently versed in modern mathematical techniques to derive important tactical lessons from the statistics of past and current operations.

On the basis of combat results and laboratory experiments, the members of the Anti-Submarine Warfare Operations Research Group established the basic laws of visual and radar sightings and devised scientific search plans which made the most of the aircraft and surface ships available and increased the probability of sightings. To keep German submarines from bringing cargoes of tin and rubber from the Far East to Europe, barrier patrols were designed to close the gap between Africa and Brazil. Similar analytical studies were made the basis for radar and sonar search plans, for air-sea rescue, and for the use of the magnetic airborne detector and the radio sonobuoy.

Operations analysts pointed out that U-boats, when they heard our pings becoming louder and faster, estimated the moment of our attack and dove below the sonar beam. The remedy for this was the creeping attack carried out by two escort vessels, the first maintaining sound contact at a fixed range and ping interval while it coached the second attacker at very low speed over the U-boat by signals.

On their side the U-boats created disturbances by backing down, turning sharply, or ejecting chemicals that generated clouds of bubbles. These reflected strong echoes and thus simulated a second or third U-boat to confuse the attacker. The Allies broadcast to their patrol craft information about this trick, and instructions to their sonar and asdic operators how to read through false targets. Futile attacks on clouds of bubbles ceased.

Because an aircraft equipped with radar has a search rate against surfaced submarines ten times that of surface craft equipped with radar, the importance of installing radar on our patrol planes was recognized early. Ten pre-production microwave sets were hastily assembled at the Radiation Laboratory early in 1942 and installed in B-18’s commanded by the late Colonel William C. Dolan, AAF, which sank their first U-boat on April 1. They formed part of the First Sea Search Attack Group activated in July, 1942, under Colonel Dolan’s command.

Fourteen more 10-centimeter sets, designed for use in Liberator bombers, were manufactured “on a crash basis” by the Research Construction Corporation and delivered to the British between August and December, 1942. These came just in time to play a useful part in the great battle in the Bay of Biscay.

3

IN the first two and one-half years of the war Doenitz’s jibe that “an aircraft can no more kill a U-boat than a crow can kill a mole” had had some truth in it. The Coastal Command had damaged upwards of 50 enemy submarines but had been credited with very few sinkings. Radar had increased the number of sightings, but the attacks, though executed boldly, lacked a knockout punch. This was provided in May, 1942, by equipping Wellington bombers with searchlights for night attacks and depth charges filled with torpex, a mixture of RDX, TNT, and aluminum — superior in destructive power to the previous depth charges by about 50 per cent. The number of long-range aircraft operating in the Bay steadily rose and the sightings and kills of U-boats mounted.

What the Germans needed was warning of the patrol plane’s approach. They got it by equipping their submarines with search receivers which told the submarine that it was being “floodlit” by radar, long before the submarine could be detected on Allied radar screens. (Search receivers outrange radar systems.) This gave the U-boats warning in plenty of time to submerge before the airplane or surface vessel came within attacking range. As soon as the search receivers got into use in September, 1942, the number of radar sightings rapidly dwindled. Unless the British could find an answer, their splendid counteroffensive seemed doomed to failure.

The answer was the 10-centimeter radar installed in aircraft and surface vessels, for the search receivers designed to pick up transmissions at 200 megacycles could do nothing with microwaves. The Nazis, formerly so confident, grew panicky as the patrol planes equipped with the new 10-centimeter sets dived on the U-boats unannounced. For a long time the Germans were at a loss. Believing the British had switched to infrared detection, they made frantic efforts to counter that.

They were disappointed at their failure to do more damage to the huge armada of over a thousand vessels which moved from United States and British ports to the coasts of North Africa. Although some 40 U-boats were lying in wait, they sank only 23 ships during November. The Germans had concentrated their U-boats on both sides of Gibraltar, mustering every submarine that could reach the area within ten days. “Defense in these African waters,” Doenitz gloomily reported, “was very effective and U-boat losses were correspondingly high.” Heads fell. Doenitz succeeded Grand Admiral Raeder as Commander in Chief at the end of January, and announced a fight to the finish. “The entire German Navy,” he declared, “will henceforth be put into the service of inexorable U-boat warfare.”

The campaign launched by the Nazis early in 1943 was indeed menacing. Desperate efforts were made to regain the ascendancy which the U-boats had enjoyed in November, 1942, when nearly a million tons of shipping were sunk. The crow had succeeded in attacking the mole. But the mole fought back. Running submerged at night along the transit routes through the Bay of Biscay or north of Scotland, the U-boats surfaced by day to speed their passage; and if attacked by patrol planes, they put up a stiff battle with their flak guns.

As the weeks passed, punctuated by staccato bursts of fighting, the number of U-boats operating in the Atlantic mounted steadily. In general, half the submarines available were in port and half at sea. Of those at sea, half were in the combat zone and half in transit. In the winter of 1942-1943 as many as 70 to 80 submarines were operating simultaneously in the combat area, chiefly in wolf packs in the 600-mile gap in mid-Atlantic, out of reach of shore-based aircraft. Allied shipping losses reached 750,000 tons in the first three weeks of March, 1943. Defending one convoy, the British destroyer Harvester rammed a U-boat but was herself disabled and sunk by two torpedoes from another craft. The Free French corvette Aconit, in company, finished off the first of the U-boats, picked up the survivors of the Harvester, and rammed and sank the submarine which had dealt the British destroyer her deathblow.

4

AT the end of March the tide turned against the U-boats. First among the factors was the closing of the gap in the mid-Atlantic. Liberators equipped with extra gas tanks and microwave radar, and navigating in part at least by loran, enabled the British, American, and Canadian air forces to establish a shuttle service between the United Kingdom, Iceland, and Newfoundland. These squadrons of Very Long Range (VLR) aircraft burst in on the wolf packs unheralded, warned and diverted our convoys, protected them like an umbrella, and soon made it impracticable for the U-boats to refuel in mid-ocean, as they had been doing with impunity. These VLR patrol planes were soon reinforced by aircraft from the new escort carriers. The first of these vessels entered the fray in March and scored its first success in April. The magnificent exploits of U.S.S. Bogue and U.S.S. Card won for these two escort carriers the coveted Presidential Unit Citation. Support groups organized around these and similar vessels took the offensive in hunting out the U-boats and harried them relentlessly.

At the same time the number of escort vessels steadily increased and their equipment improved. Admiral Cochrane’s superbly executed destroyerescort program paid big dividends. The DE’s swarmed on the convoy routes, admirably equipped with centimeter radar, with sound gear for close-in detection, and with the spigot mortar for “hedgehog” attacks with forward-thrown, faster-sinking torpex depth charges. Smaller surface craft made good use of the mousetrap rocket. By June, 1943, the U-boats had largely withdrawn from the North Atlantic. Speaking at the Guildhall on June 30, Prime Minister Churchill proudly announced that hardly a single Allied ship was sunk in the North Atlantic between May 17 and the end of June.⁴

When U-boats used their radio to assemble a wolf pack, the location could be plotted by British and American Huff Duff stations. Land-based and carrier-based aircraft equipped with radar soon scoured the area. If the U-boat submerged, the planes parachuted several expendible radio sonobuoys whose hydrophones could detect U-boat noises. These activated the radio transmitter, which summoned near-by planes or surface escorts to close in and start their search with sonar or asdic.

It was clear from intelligence reports, however, that the battle was not over. The Germans were fitting their U-boats with radar to detect approaching aircraft and with greatly increased anti-aircraft armament. They had also instructed their submarine commanders to make less use of their radio, to prevent location by the Huff Duff. The Luftwaffe started long-range fighter patrols in the Bay of Biscay, which the British countered with Beaufighters and Mosquitos. The battle raged in the skies as well as on and under the surface. In August the Germans startled the world with the first successful guided missile, the glider bomb HS293, and followed it almost immediately by the Gnat acoustic homing torpedo.

This formidable weapon might have taken a far heavier toll had its introduction not been anticipated by Allied scientists. Effective countermeasures were ready.

A great improvement in the coverage in midAtlantic came when the Coastal Command, at the end of October, 1943, began operating VLR aircraft from Terceira in the Azores. By this time, U-boats were beginning to adopt more cautious tactics, for their losses had been staggering. In the last four months of 1939 they had lost 9 submarines; in 1940, 22; in 1941, 35; and in 1942, 85. All these losses were more than offset by new construction. In the single month of May, 1943, 42 were sunk, a net loss of 22, since only 20 new craft were completed. For the whole year 1943, the total of German losses reached 237. In such a struggle, moreover, the more daring commanders were likely to be the first to be lost, for they pressed home their attacks more boldly.

Aircraft had played the foremost role as submarine killers, thanks to their high search rate, their admirable microwave radar, and the new weapons they carried. They had used magnetic airborne detection effectively to cork the Straits of Gibraltar, had employed with success the radio sonobuoy and other secret airborne devices, and had found the rocket an excellent anti-submarine weapon.

“For some months past,” wrote Grand Admiral Doenitz on December 14, 1943, “the enemy has rendered the U-boat war ineffective. He has achieved this object, not through superior tactics or strategy, but through his superiority in the field of science; this finds its expression in the modern battle weapon — detection. By this means he has torn our sole offensive weapon in the war against the AngloSaxons from our hands. It is essential to victory that we make good our scientific disparity and thereby restore to the U-boat its fighting qualities.” ⁵

Despite this note of gloom, and the heavy losses in submarines during 1943, the Germans opened the campaign of 1944 with more U-boats than ever. They had equipped them not only with radar to detect approaching airplanes, but with heavy antiaircraft armament to shoot them down, and with the Naxos search receiver designed to pick up 10centimeter radar transmissions. This device fortunately did not prove nearly so effective as they hoped, but the vigor of the Nazis’ counteroffensive on the scientific front is attested by the fact that they had made good progress with a search receiver for 3-centimeter radar.

5

IN the early months of 1944 it was clear that Doenitz was husbanding his U-boats in the hope that they might play a decisive part in repelling the impending invasion of Europe. In the meanwhile he fitted a considerable number of them with Schnorkels. This retractable air intake and exhaust pipe could be raised or lowered from inside the boat. It enabled the U-boats to run on their Diesels at periscope depth, charging their batteries while submerged.

Elaborate precautions were taken to coat the top of the Schnorkel with a camouflage which it was hoped would not reflect a radar echo. This pipe, projecting above water a little lower than the periscope, was a difficult target for aircraft to detect and attack. Although its use increased the discomfort of the crew, U-boats managed in the closing months of the war to operate for weeks at a time without surfacing. Personnel on board received vitamin pills and daily sun-lamp treatments to preserve their health.

On their side, the Allies greatly increased their patrol vessels and aircraft, drilled their sound men so that they would not be duped by German sonic decoys, and installed airborne search receivers for intercepting and homing on enemy radar transmissions. Much attention was also given to the coördination of air and surface attacks.

In May, the Coastal Command, reinforced by American Air Force and Navy squadrons, opened a brilliant offensive in Norwegian waters against the U-boats that were leaving to join the forces of the Kriegsmarine in the Bay of Biscay for a joint attack on our invasion forces in the English Channel. The pursuit ranged widely over the Eastern Atlantic and into Arctic waters, and few U-boats got through. Those that did joined up with U-boats based on French ports for a bitter struggle in the Channel and the eastern portion of the Bay of Biscay, fighting back desperately with their anti-aircraft guns against the increased attacks from the air. Taking heavy losses, they were unable to interfere with the greatest of amphibious operations, and it was ten days after the landings in Normandy before the first U-boat was operating on Schnorkel in the combat zone.

After June 8 few U-boats were caught on the surface, and Allied patrol craft resigned themselves to endless searching for periscopes, Schnorkels, and oil slicks. In this wearisome hunt, microwave radar of high resolution proved its value again and again, and the radio sonobuoys gave the flyers extra ears for use under water. Few U-boats got through to our shipping lanes, and many paid for the attempt with their lives. As a historian of the Coastal Command well said, “The weapon which was to cut our communications in the Atlantic had failed even to cut them in the Channel.”

As the advance of the Allied Expeditionary Forces made it clear to the Germans that they would soon lose the use of the French coast, they began to send the U-boats northward, producing a new flock of hard-fought actions. A few, by using Schnorkel, penetrated into the Channel, but only nine ships out of the thousands operating there were sunk by U-boats.

In the last phase of the European war the Germans tried to complete for duty two new types of submarine: a heavy cruiser of 1500 tons with high underwater speed, and a smaller craft of 300 tons. By this time the steady pounding from the Eighth Air Force and the RAF had hamstrung German industry and the war ended before these new craft could be tested in action. In the last month of the European war the U-boats made a determined effort to break through in considerable strength to our Eastern seaboard, but they lost five submarines in the attempt and were not successful in reaching their goal until, after V-E Day, they came in peacefully to surrender.

After Doenitz’s tribute to the part played by Allied scientists in the defeat of the U-boat it is almost superfluous to say more. The figures of German losses in submarines, and Allied losses and gains in merchant shipping, are these: —

6

THE pattern of subsurface warfare in the Pacific was very different from that in the Atlantic. The Germans, regarding the submarine as their best weapon against Britain and the United States, concentrated their naval effort on the use of the U-boat as a commerce destroyer, and almost won the war with it. Although convoys proved a countermeasure of the utmost importance, their use resulted in a great slowing down of shipping. The fastest ships, relying on their speed, could in general sail independently. A convoy had to sail at the speed of the slowest vessel, over routes which were generally longer than normal.

The great danger from the U-boats made Allied operations in the Atlantic, until the landings in Normandy, largely a defensive operation, though the RAF and Royal Navy took a heavy toll of German shipping through bombing, mining, and surface attacks. The Allied task primarily was to put more and more pressure on the U-boats until a point was reached at which they could stand it no longer and would quit until they could develop new tactics. So severe was our counteroffensive that the German submarine forces took losses two or three times as heavy as those they used to consider excessive in the First World War. But still the U-boats kept coming out and their crews did not mutiny.

The Japanese had at one time about 70 oceangoing submarines, whose speed of 22 knots on the surface and 8 knots submerged compared favorably with submarines of other nations. They could not safely dive as deep as German or American craft, but they fought to the limit. Our anti-submarine craft pursued them with equal vigor and one of them, the U.S.S. England, set a war record by destroying six submerged Japanese submarines in a period of eleven days with the help of sonar gear.

The Japanese used their submarines for two primary purposes: as adjuncts to their fleet and to supply cut-off bases. The latter, as events showed, had no great effect on the course of the war, but the Japanese submarines inflicted heavy losses on our naval vessels. They sank the Yorktown and the destroyer Hammann at Midway, the Wasp on September 15, 1942, and torpedoed the Saratoga twice during the first year of the war. They damaged the heavy cruiser Chester and many other craft, sank the anti-aircraft cruiser Juneau on November 13, 1942, the escort carrier Liscome Bay a year later, the destroyer escort Shelton in September, 1944, and the heavy cruiser Indianapolis on July 30, 1945. Against our own submarines they proved Japan’s most effective weapon.

Their losses were heavy: 3 in 1941, 22 in 1942, 21 in 1943, 35 in 1944, and 24 in 1945. Of these 105 submarines sunk or captured at sea, 23 were credited to United States submarines in Admiral King’s reports, and two to British submarines.

Although the protection of our task forces against submarines remained a problem requiring destroyerescort and combat air patrols, and affording an opportunity of using some of the advanced techniques developed in the Atlantic, the protection of merchant ships from underwater attack was not a major task for us in the Pacific. Small, special convoys operated between San Francisco and Pearl Harbor, San Francisco and the South Sea Islands, Seattle and Alaska, and Seattle and the Aleutians, but practically all of our shipping in the Pacific was able to operate independently.

The destruction of commerce by submarines was a major part of our Pacific offensive. The lack of sufficient shipping to tie together effectively her sprawling empire was Japan’s weakness, and we attacked shipping relentlessly, by every means at our disposal. Here our submarines proved our best weapon. “At a conservative estimate,” declared Admiral King, “they sank, in addition to many combatant ships, nearly two thirds of the merchant shipping which Japan lost during the war. They made it more difficult for the enemy to consolidate his forward positions, to reinforce his threatened areas, and to pile up in Japan an adequate reserve of fuel oil, rubber, and other loot from his newly conquered territory.”

Including only enemy merchant ships of 1000 tons or over, our submarines destroyed by gunfire and torpedoes over 1000 vessels, of so much tonnage that by the end of the war the Japanese merchant marine had virtually ceased to exist.

Our submarines took the offensive from the beginning of the war in the Pacific. Admiral King credited them with eliminating one battleship, the Kongo, the carriers Soryu, Shinano, Shokaku, and Unryu, the escort carriers Chuyo, Jinyo, Otaka, and Unyo, the heavy cruisers Atago, Kako, and Maya, 9 light cruisers, 43 destroyers, and 189 smaller vessels. They also performed reconnaissance, rescue, supply, and lifeguard duties, evacuated personnel from Corregidor, and delivered supplies and equipment to guerrillas in the Philippines. They rescued more than 500 aviators and provided intelligence of the utmost importance. The advance information furnished our surface and air forces prior to the Battle of Leyte Gulf played a large part in that victory.

Considerations of security preclude a detailed analysis of the many contributions of the NDRC to the effectiveness of our submarines. In addition to equipment, the careful studies of underwater conditions and the maps based on them enabled submarine commanders to hide at times over rocky bottoms in tropical waters where snapping shrimp made a noise that masked the sound of the submarine. Many other fish, including croakers and drummers, contributed to the bedlam in shallow waters.

Temperature gradients were not likely to affect asdic ranges seriously around the British Isles, but they were troublesome for the stalker of submarines in the Mediterranean and even worse in Japanese waters. The bathythermograph became standard equipment on submarines, which by means of this instrument could seek out a suitable temperature gradient, or thermocline, and hide there with less risk of detection.

The war cost the Allies 4773 merchant ships of 23,000,000 gross tons sunk by enemy action. A total of 996 Axis submarines were sunk, and 221 large and scores of midget submarines fell into Allied hands after V-E Day and V-J Day. The British received credit for sinking 70 per cent of the enemy submarines, and the United States credit for 30 per cent.

These figures give but an imperfect idea of the stakes of the game. The defeat of the U-boats made it possible to keep supplies flowing to Great Britain and Russia and to transport to North Africa, Italy, and France the armies which forced Germany to surrender. In the Pacific the Japanese submarines failed, in the long run, to interfere with the freedom of Allied naval forces to operate where and when they chose. Allied submarines, on the offensive from the outset, destroyed the maritime communications which were the weakest link in the Japanese Co-prosperity Sphere. Once they were gone, it fell apart like a house of cards, leaving the main islands exposed to attacks by sea and air that reduced Japan’s cities to ashes.

When the war in Europe ended, the Germans were able to send to sea submarines which could operate for weeks without surfacing and could make such high speed under water as to upset the whole Allied defense system. Even without atomic power and atomic missiles the submarine remains a most dangerous weapon. With them, it might prove more formidable than the long-range bomber. If we make mistakes enough in the post-war years, a revived Germany or some other European power might think it could win the dominion of the world as Germany twice so nearly did by subsurface warfare. Batters have been known to hit a home run with two strikes against them.