part two is here

Once in awhile it’s fun to do some thought experimentation. I mentioned a few days ago that I was mulling over the similarities between the counterinsurgency problem in Iraq and how the American, Canadian and British navies finally defeated the U-boat threat in World War II.

The United States declared war on Japan on Dec. 8, 1941. Germany and Italy, already allied with Japan, declared war on the United States on Dec. 11. The Roosevelt administration had been expecting it since the Pearl Harbor attack. In response, President Franklin Roosevelt sent a message to the Congress the same day requesting “the Congress to recognize a state of war between the United States and Germany, and between the United States and Italy.” Congress complied before ending that day’s session.

Defeating Germany required transferring mountains of war materiel and millions of soldiers from the US to the European theater, mainly to North Africa and the British Isles. Since aircraft of the day were entirely unable to move the troops or materiel, the US embarked on a massive shipbuilding program for cargo and commandeered passenger liners such as Queen Mary to move troops.

Hitler’s military knew, of course, that the US would have to reach Europe by sea. Germany’s plan was to repeat what they had almost pulled off during World War I: use submarines (German unterseebooten, hence “U-boats”) to interdict the sea lanes and defeat the Allies by sinking their ships. The Germans also sailed surface raiders such as Bismarck and Graf Spee early in the war, but they were sunk by the Royal Navy sank or neutalized. The Luftwaffe, using Kondor attack bombers, was a deadly and successful enemy when ships reached the Western Approaches to the Isles, but the planes did not pose the enduring threat that U-boats did.

Winston Churchill wrote after the war of the Battle of the Atlantic, as the antisubmarine warfare was called, “The only thing that ever frightened me during the war was the U-boat peril.” Not only was by sea the only way to move American men and materiel to Britain, Britain’s very survival depended on seaborne importation of foodstuffs and raw materials, principally from America.

The German U-boat flotilla was far from prepared for the task thrust upon it at the war’s open in September 1939. The admiral commanding the U-boat fleet, Karl Doenitz, had counted on having 300 subs under his command by the time war began. But Germany possessed fewer than 100 submarines when the war opened; of these only 58 were usable for combat patrols. Production accelerated. By May 1942, Germany had more than 300 U-boats with about 100 on operational patrol on any given day, though not all in the Atlantic.

On Sept. 3, 1939, the U-boat U-30 sank the liner Athenia northwest of Ireland. Historians consider the event the beginning of the Battle of the Atlantic. The sinking, however, was an error by U-30’s commander, who mistook the liner for a armed merchant cruiser. The British Admiralty responded by ordering full convoy operations be put into effect.

Convoys, large numbers of ship sailing together under a unified command, had been devised in World War I as a defense against U-boats. Their advantage lay solely in the fact that the Atlantic is so enormous that a convoy even of dozens of ships was not really easier for a U-boat to find than a single vessel. Besides, there would never be enough destroyers and corvettes to escort single vessels. Convoys grew in size as the war continued. Only very fast ships such as Queen Mary were be permitted to cross the sea alone, on the supposition that they were fast enough to outrun any U-boat that might detect them (which proved correct).

The first month of the war, September 1939, was a grim foretaste of what was to come. The allies lost 21 ships totaling more than 110,000 tons, including one fleet carrier, while sinking only two U-boats. It would only get worse.

The sea proved to be a fantastic place to hide for U-boat commanders. If whole convoys were difficult to find, think how greater the U-boat hunting problem was for Allied commanders. Usually the only way convoys learned a U-boat was nearby was when their ships started blowing up and sinking.

In June 1940 Admiral Doenitz devised a new tactic for his boats. He called it Rudeltaktik , or “pack tactic,” which the Allies called “wolfpack.” Doentiz ordered submarines to patrol in lines to look for convoys. When a U-boat discovered a convoy, it would shadow it and report its speed and heading to “Admiral U-boats,” as Doenitz’s headquarters was known to U-boat crews.

Admiral U-boats would then signal boats in reasonable vicinity to converge on the convoy and make a coordinated attack. This tactical innovation devastated convoys. Wolfpacks varied in size from only a few U-boats to 20 and sometimes more. Convoy ONS-5, for example, was attacked by a wolfpack that finally amounted to 55 U-boats in April 1943 in a convoy battle lasting two weeks. ONS-5 lost 13 ships totaling just under 62,000 tons. The month before, 43 U-boats sank 93,500 tons of convoy HX-229. These convoy battles were not hit and run affairs. They usually lasted many days, often more than a week.

By June 1942 Allied shipping losses were of grave concern to the British and Americans. The Allies were in a race with Germany to build ships and fill them with materiel faster than the U-boats could sink them. With the advent of the Liberty ship, American shipyards could win that race, barely, and would start to do so in July. But Allied commanders realized that construction was not the way to win the battle. The human toll of ships’ crews could not be sustained. They had to develop much more effective antisubmarine weapons and tactics. By the end of 1942 the Allies had lost more than 5.5 million tons of shipping since war’s beginning. In January 1943 at the Casablanca Conference, Prime Minister Churchill and President Roosevelt agreed that defeating the U-boats had to take top priority.

Even so, the best days for U-boats were yet to come, at least in the minds of U-boat commanders. By March 1943 the U-boat fleet numbered 400 submarines, of which more than 250 were patroled various fronts. (Hitler had ordered many boats stripped from Atlantic patrol to protect Norway and the Mediterranean theater used many U-boats, too.) One of the few U-boat captains to survive the war, Herbert Werner, wrote in his book Iron Coffins, that,

This March of 1943 was the greatest month of U-boat history; our boats had sent to the bottom almost 1 million tons of Allied shipping.

But there were ominous signs, Werner wrote.

[O]ur triumphs were now being wrenched from the enemy with a difficulty unknown in previous years. As the size of convoys increased, the coordination of British and American naval units had sharply improved their convoy defenses. Escort vessels of a new type, the swift and highly maneuverable corvettes, increased the hazards of U-boat attacks. Most ominous of all was the plague of enemy aircraft. More and more planes were flying ever farther to sea and bombing out boats on the homeward run or outward bound with ever-deadlier accuracy. …

As I saw it, the whole war now hinged on our U-boat effort in the Atlantic.

The U-boats’ glories of March 1943 turned to their abattoir in May, when the Allies’ ASW efforts finally came together. From that month to the end of the war the Allies always held the initiative and defeated the U-boats with increasing effectiveness.

In May Werner, executive officer of U-230, went back into the Atlantic.

May 5. … Riedel handed me the deciphered message in silence: DESTROYER. ATTACKED. SINKING. U-638. This report was the last act of U-638. Nothing was heard of her again.

Two hours later, a fresh distress signal was hastily decoded; ATTACKED BY DESTROYERS. DEPTH CHARGES. LEAVE BOAT. U-531. …

May 6. … another signal … ATTACKED BY CORVETTE. SINKING. U-438. …

Now another was intercepted: AIRCRAFT. BOMBS. RAMMED BY DESTROYER. SINKING. U-125.

So it went for the rest of the month. Before the end of May the Allies had sunk 40 U-boats (Werner says 43), more than any month of the war and twice the rate at which Germany was building them. Shocked, Admiral Doenitz ordered a standdown of U-boat operations during June to gain time to fit his subs with new equipment, none of which proved efficacious in turning the tide. By the end of the year, wrote Werner, the sea supremacy that U-boats had enjoyed for two and one-half years had been wrenched away by the Allies in only seven months.

What turned the tide?

There were a number of factors that enabled the Allies to defeat Germany’s submarine threat. They all boiled down to locating the U-boats and relentlessly attacking them until they sank. The main keys of victory were:

1. Signals intelligence, especially the codebreakers at England’s Bletchley Park who cracked the German naval Enigma codes as part of the Ultra operation. This feat enabled the Allies to read most of Admiral U-boats’ instructions to its boats. This success was not certain or uniform, though; there was a 10-month gap in Ultra intelligence when the Germans made a major change of encoding. (The Germans also cracked many of the convoy codes the Allies used.)

2. Improved technology in submarine detection. When surfaced, U-boats used a radar-detection device called Metox to detect the 1.5-meter-wavelength radar of Allied aircraft, their severest threat. Metox never worked perfectly, and initially unknown to the Germans Metox itself was an emitter. Allied scientists fitted bombers with gear that detected Metox transmissions, enabling the aircraft crew to guide themselves to the U-boat. Many U-boats were lost that way. Finally Admiral U-boats ordered all Metox use discontinued.

Then the Allies introduced for aircraft centimetric radar, which enabled bomber crews to detect U-boats from much longer ranges than before, certainly from beyond visual range. Accurate radar also meant that nighttime no longer offered a cloak for U-boats to run on the surface using diesel power while recharge the batteries used to propel the U-boats underwater. Extremely powerful lights called Leigh lights were fitted to the bombers as well to illuminate the U-boat on the bomb run. Finally, U-boats began sailing underwater all night and on the surface during the day. It was but a temporary reprieve.

Then there was the “huff-duff,” the nickname for high-frequency, direction-finding radio receivers. The widespread use of these very accurate devices enabled Allied operators to locate the source of German transmissions practically in real time. Herbert Werner wrote of a day when his U-boat and one other were refueled at sea by a supply submarine. After they parted company, the supply sub’s captain stupidly radioed a status report to Admiral U-boats. The supply sub was sunk six hours later.

3. ASW weapons technology continued to improve. The old “oil barrel” style depth charges used early in the war gave way to new types such as the hedgehog that enabled near-360-degree dispersion around the launching vessel, and in large numbers launched at one time. Fuzing was changed so that instead of detonating at a preset depth, calculated (guessed) by ASW officers, the depth charge exploded only when it hit the U-boat. This feature kept the surface ships’ sonar clear of explosion-generated noises, enabling continuous tracking of the U-boat and removing doubt about whether it had been hit. Sonar itself continued to improve over the course of the war.

The mass introduction of corvettes, mentioned by Werner, played a major role. Corvettes were ASW vessels of less than 1,000 tons displacement. They were miserable rides for their crews but terrible foes of U-boats.

4. “Intentional lethality.” For at least the first couple of years of the war, British warships attacked U-boats more to neutralize their threat rather than actually destroy them. Finally they awakened to the need to sink the U-boats rather than simply drive them away from the convoy. Some units of warships assigned to convoys were ordered to locate attacking U-boats and pound them until they sank; different hunter-killer teams would relieve one another above the U-boat concerned. Werner reported that his U-boat barely survived a relentless depth-charge attack of more than 36 hours and more than 300 counted depth charges. Most U-boats did not survive such attacks.

Submariners of every nation of the war agreed that their worst nemesis was aircraft. From the time a lookout on a surfaced submarine spotted an enemy plane until the plane attacked was three minutes or less, sometimes less than a minute. Werner reported that in one such attack his U-boat crash dived to escape but the plane’s bombs literally blew the U-boat above the ocean’s surface. It fell back into the water where it foundered helplessly. The plane flew away, though, apparently out of weapons.

In 1940 (IIRC) Churchill ordered catapults to be fitted to some merchant ships to sling fighters off when a surfaced U-boat was detected. There was no way for the plane to land and more than a few pilots were lost ditching near their mother ship. It was a dunderheaded idea but a measure of British desperation against the U-boats. Finally, the Allies started sending escort carriers along with convoys, small carriers that could launch, recover and refit airplanes. This idea worked so well that eventually six fleet-carrier battle groups were assigned to cross-Atlantic duty.

The four-engine, B-24 “Liberator” bomber was a great success in ASW. It was speedy for a bomber and very long ranged. By 1944 all the major Atlantic convoy routes were wholly ranged by Liberators as new bases were developed. Werner wrote that the B-24 was probably the most feared of all Allied aircraft.

All these things worked together to enable Allied airmen and sailors to do one thing: find and kill submarines. Although there were never any precision-guided munitions developed in the war for ASW, the net effect of the technology, weapons , doctrine and training very much rendered Allied ASW efforts a precision-driven affair.

What has all this to do with counter-insurgency warfare? Stay tuned.

Endnote: Former American sub officer Mike Lief takes a look at present-day German submarine technology, and pronounces it worrisome.

part two is here