WORLD SUBMARINE HISTORY TIMELINE
1580-2000

Prepared for NOVA by Captain Brayton Harris, USN (Retired)
Author, The Navy Times Book of Submarines: A Political, Social and Military History

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1580-1869

1870-1914

1914-1945

1945-2000

 

1914
The skipper of a British destroyer found himself sitting above a U-boat he could see, but not touch. "What we need," a staff officer mused, "is some sort of bomb to drop in the water." Thus began development of the depth charge, which claimed its first victim in March 1916. However, overall, these depth charges were not very effective unless exploding quite close to the U-boat; say, about the length of your living room. The main benefit was psychological.
1915
The British blockade began to have a telling effect, and Germany vowed to mount a counter-blockade, using submarines. However, the German Navy had to wrestle with a serious ethical and legal dilemma. Under international law, a warship could stop and search a merchantman; if found to be carrying contraband cargo for an enemy, the ship could be captured and a "prize crew" set aboard to sail her to an appropriate harbor. Under some circumstances, the ship could be sunk, provided that the crew had been allowed to take to the lifeboats first.

A submarine did not carry enough sailors to make up prize crews, so the only option was to sink the merchant ship. For this purpose, submarines were equipped with deck guns. However, if the submarine came to the surface to give fair warning, she herself became vulnerable to attack (by ramming, by concealed guns, by warships rushing to the rescue).

German policy went through several cycles: play by the rules for a time, but in February, in retaliation for the indiscriminate damage of the blockade, she opted for "unrestricted submarine warfare." The legal requirement for "fair notice" was met, at least in theory, by setting specifically-designated war zones, within which all vessels were subject to attack without warning.

With only 35 active U-boats, Germany began sinking British merchant ships faster than they could be built, and got very serious about submarines. Several accelerated construction programs were launched; one was for smaller, less capable boats which were nonetheless well-suited to operations close to home. These were dubbed the UB-Class..


In this post-war photo, a French boat is on the left. Next, a German late-model coastal boat UB-133, and an early model UB-24.
1915
In May, U-20 sank the civilian passenger liner "Lusitania," killing 1,198 men, women and children. Germany did not want to provoke the United States, and under pressure of international public opinion, backed off – for a while. In February 1916, unrestricted operations were resumed, but were cancelled in April after a controversial attack on a civilian ferry boat. Nonetheless, the U-boats were by then taking out about 300,000 tons of shipping a month.
1915
The British discovered that torpedoes were routinely running under their targets; they finally realized that the explosive warhead weighed forty pounds more than the peacetime practice head upon which torpedo depth settings had been based. They were not the only nation – and this was not the only war – in which serious problems with the design and operation of torpedoes would impede progress. See below.
1916
Germany created the ultimate World War I U-boat: a true long-range submarine cruiser. Boats of the UA class were 230 feet long, about 1500 tons with a speed of 15.3 knots on the surface, and a range of 12,630 miles at 8 knots. Armament: Twin 150 mm (5.9 inch) deck guns, 1,000 rounds of ammunition, nineteen torpedoes, manned by a crew of 56 with room for twenty more.

Forty-seven UA boats were ordered, but only nine made it into service before the November 1918 armistice.

One of the first of the UA-class was built as a blockade-breaking civilian cargo submarine operated by the North German Lloyd Line. "Deutschland" had a cargo capacity of 700 tons (small if compared with surface ships, but equal to that of seven 1990-era C-5A airplanes). She engaged in high-value trans-Atlantic commerce, submerging to avoid British patrols; on her first trip, she carried dyestuff and gemstones to America, nickel, tin and rubber (much of it stored outside the pressure hull) back to Germany.
 


The cargo-carrying submarine "Deutschland" at New London, CT, in November, 1916, on one of her two "civilian" visits to the United States; three months later she had been converted and sent to war as U-153.
 1916
Toward the end of the year, the situation in Germany was getting desperate. The typical daily food ration was "five slices of bread, half a small cutlet, half a tumbler of milk, two thimblefuls of fat, a few potatoes, and an egg cup of sugar."

"If we were to starve like rats in a trap," wrote one German citizen, "then surely it was our sacred right to cut off the enemy's supplies as well."
 1917
In February, the German government announced total unrestricted submarine warfare. A note to the U. S. government affirmed that "England is using her naval power for a criminal attempt to force Germany into submission by starvation," and warned that Germany was now compelled to use "all the weapons which are at its disposal." The German government knew that this would most likely bring America into the war, but predicted that Britain would be forced to the peace table before American forces could have much effect.

Also in February, in one of those strange parallels in which history occasionally delights, another Housatonic was sunk by an enemy submarine – in this case, an American merchantman; the attacker survived.

Great Britain had the worlds largest merchant fleet, almost half of the world total, but British shipbuilding capacity was only about 650,000 tons a year. By March, U-boats were sinking almost 600,000 tons a month and Great Britain was down to a six-week food supply.

The U. S. entered the war in April.
 1917
There was one time-honored method for protecting merchant ships from enemy attack: convoy, dating back almost to the dawn of ocean commerce. However, the British Navy resisted: there were too many ships coming and going, 2500 a week, and port facilities were already strained; bringing in the glut of a convoy would create chaos. The convoy would become a huge target for the U-boats. Convoy might be all right for military auxiliaries such as troopships, but merchant crews did not have the skills necessary to keep in convoy formation, and many did not speak English. Most merchant ships were fast enough to outrun a U-boat. Besides, and perhaps most significant, warships should be out looking for the enemy, not herding bunch of merchantmen. The Navy was trained for offense, not defense. To be aggressive, not passive.

The counter arguments: most of the traffic was made up of small coasters and ferries; there were only about 140 trans-ocean ships arriving each week, spread across a number of ports. A U-boat could only make one attack before the escorts would force it to break off and hide – the larger the convoy, the more ships home free. A merchant might outrun one U-boat – right into the arms of another. Crews could be trained. The goal was to curtail sinkings, not make naval officers feel good.

By late spring, the situation was grave enough that the Navy finally agreed to a trial of convoy. And never looked back. Of 83,959 ships in convoys from then to the end of the war, only 257 were sunk by U-boats. During the same period, 2,616 independent sailers were sunk. The main benefit of convoy: it forced the U-boats to attack, submerged, which meant that they already had to be in attack position if a convoy happened to sail past.

Convoys with air patrol were the safest of all – because the submariners knew that, even if they carried out an attack, the aircraft could determine their approximate location by tracing back down the visible torpedo track. However, the carrying capacity of most aircraft of the day was too limited for heavy weapons. Many could not even carry a radio set.
 
 1917
Six UA boats were deployed to the East Coast of the United States, where they laid mines and sank 174 ships – mostly smaller vessels without radios which could neither be warned or give warning. The UA- boats proved that a submarine could operate 3000 miles from home base, but did not have any impact on the movement of troops and supplies to Europe.

Twelve American submarines took up station off Ireland and in the Azores. They had nil effect on the war, but learned a lot about wartime operations. (The primary wartime contribution of the U. S. Navy was anti-submarine patrol – providing 80 percent of all trans-Atlantic convoy escorts.) One clear lesson: the dive time of the American boats was too slow; for the L-class, it averaged 2 minutes 23 seconds. A small UB could be fully under in 27 seconds.
 



Most navies adopted an alpha-numeric system for identifying submarines, referring to the class and the series within the class: A-1, L-5, and so forth. The U. S. Navy added names to some (but not all); in the 1920s, the scheme had reached S-51 (the 162nd U. S. submarine). Thenceforth, a different system was followed: U. S. submarines carried a hull number and name (usually that of some sea creature), i.e. SS-163, "Barracuda." The British system: A.5, E.6. Germany did not differentiate class, only type: all hull numbers began with U-, with type distinctions such as UA, UB, UC.

Shown here, U.S. Navy L-class boats, stationed in English waters in 1917. The prominent "AL" identifier was to avoid confusion with boats of the British L class.

 1917
"Pattern" camouflage was designed to confuse a U-boat's visual fire-control systems – making it difficult to judge range, size, speed, and course. This practice continued into World War II, when more sophisticated systems were introduced.

Submarines themselves employed more natural schemes of camouflage, typically to blend in with operating conditions: white for arctic waters, different shades of gray for different parts of the world. Eventually, all navies adopted some version of the U. S. Navy's "haze gray" for surface ships, black for submarines.
 

The American troopship Louisville in full-dress. For the record, not one soldier was killed by U-boat while being transported – always in convoy – either across the Atlantic or across the English Channel.
 1917
One vulnerability constantly exploited by the Allies and not fully appreciated by the Germans: radio intercepts. The Germans knew their transmissions could be overheard and U-boat locations pin-pointed by direction finders, but didn't seem to care: they assumed the U-boats would be long gone before any attackers could arrive on the scene. They didn't realize that by knowing where the U-boats were operating, the Allies often could re-route convoys out of harm's way.
 1917
Great Britain introduced the steam-powered K-CLASS. These huge boats – at 338 feet and 1883 tons, three times the size of any other in the fleet – were built in response to intelligence reports that Germany was building a 22-knot submarine. The reports were in error.

So were the K-boats. They took eleven minutes to dive; temperatures in the boiler room then reached 160 degrees F, and in the engine room, 90 degrees F, although, since the engines were not running, no one needed to be in those spaces while submerged. Naval planners were not concerned about the excessive dive time – they assumed that the submarine crews would see the masts of approaching ships well before the enemy could spot them.

Naval planners seem not to have noticed the introduction of the airplane and airship to the equation.
 
 1918
The development of submarine-locating devices began early in the war with hydrophones (a directional microphone in the water) to listen for the sounds of propellers, and, too late to be of much use in this war, an echo-ranging system (the British dubbed it ASDIC – which apparently stands for nothing in particular – but now known universally as SONAR, which stands for "Sound Navigation and Ranging.") By sending out an audible "ping" and measuring the echo return, an operator can determine the range and bearing of a submarine.
 

1918
By summer, much of Germany was in rebellion, and the government began to move toward armistice. In October, the surface navy refused to go to sea for one last suicidal battle. The U-boat navy remained loyal; U-135 was even on alert to attack a renegade German battleship. Last kill: UB-50 sank the British battleship Britannia two days before the November 11 armistice.

SCORECARD: Germany started the war with 26 operational boats and added 390. At war's end, 171 new boats were in the water and another 148 were under construction. Wartime losses: 173. Mines took out at least 48; depth charges claimed 30; gunfire, 20; ramming 19; submarines 17; accident, 19; unknown, 19; aircraft 1.

In the meantime, U-boats had sunk more than 4,000 ships, more than 11 million tons – fully one-fourth of the world's total supply. In essence, unrestricted submarine warfare almost won the war for Germany. But Germany lost the war – because of unrestricted submarine warfare.

A paradox? No, a matter of timing. If the U. S. had not entered the war in 1917, Germany likely would have been able to force a peace agreement. But the U-boat operations directly and specifically brought America into the conflict.

Virulent wartime propaganda to the contrary, there was only one verified U-boat atrocity during the war: the sinking of the hospital ship Llandovery Castle by U-86 and the skipper's attempt to hide the evidence by machine-gunning the survivors in the water. He missed a few. Post-war, he fled the country to avoid a 1921 war crimes trial; two of his officers were tried and convicted as accessories. They did not remain too long in jail, somehow managing to "escape" their German guards within a few months.

 
 

1919
UC-97 became perhaps the only German submarine to be sunk within the continental United States. One of five U-boats turned over to the U. S. Navy for post-war study, she toured the Great Lakes as part of a Victory Bond drive, and was sunk (on purpose) in Lake Michigan a few miles east of Chicago.

Post-war, the U. S. Navy began applying lessons-learned – from operations and from a study of the captured U-boats – toward new submarine designs. Whereas the operating areas for the European powers were primarily close to home, the primary operating area for the U. S. Navy was the Pacific Ocean. Thus, the Navy needed a boat with good sea-keeping qualities, exceptional range, high reliability, and a reasonable level of habitability

 1919
Japan, emboldened by their surprise victory over the Russian colossus in 1905 and their successful role in providing escort services in World War I, began planning for an eventual showdown with the nation they viewed as their major and logical adversary: the United States. As one of the World War I allies, Japan received seven of the surrendered U-boats but went a bit beyond mere "examination." Japan imported some 800 German technicians, engineers and naval officers to teach them how to design and build submarines.
 

1919
Several unfinished K-boats were converted from steam to diesel power. One, designated M.1, was fitted with a 12-inch naval rifle. In theory, the gun could be fired while submerged; in practice, the boat had to surface after each shot to reload the gun. M.1 sank after a collision in 1925.

Another, designated M.2, was turned into a submarine aircraft carrier. M.2 sank when the hangar door was opened by mistake while the boat was still partially submerged.

 


The big gun gone underwater: the British M.1.
 1919
The Treaty of Versailles blocked the German Navy from submarines, and limited the number of officers to 1500. One of those was U-boat-skipper Karl Doenitz. He was assigned as commanding officer of a torpedo boat – a submarine on the surface, if you will. He began developing submarine tactics for the next war.

In secret, Germany acquired a Dutch shipbuilding company which designed submarines ostensibly for sale to international customers but which also were prototypes for the next class of German U-boats. In fact, 1931 sea trials for three boats sold to the Finnish Navy were conducted by German crews.
 1923
Most major navies have tried to use submarines as aircraft carriers – never with much success. Here, S-1 (the 105th U. S. submarine) was equipped with an on-deck hangar and the Martin MS-1 seaplane. Wishful thinking; the MS-1 had to be disassembled to fit in the hangar and put together again before flight, forcing the submarine to remain exposed for too long. In addition, launching and recovery were virtually impossible in the open ocean.
 
 1925
British tested the 3,000 ton X.1. armed with four 5.2 inch guns and six 21-inch torpedo tubes. This was an attempt to build an underwater cruiser. It was not successful, and was scrapped.
 

1925
U. S. submarine S-51 was rammed by a steamer and sunk in 130 feet of water.

Two years later, S-4 was rammed by a Cost Guard cutter. There was no way that any survivors might have been rescued, and these accidents led to the development of the McCann submarine rescue chamber – and an increase in the submarine hazardous duty pay instituted by T. Roosevelt in 1905.

 1927
Another "Nautilus" – the 168th American submarine, laid down in 1927 – was another effort at putting big guns on submarines; in this case, twin 6-inch. "Nautilus" offered at least one improvement of the British and French efforts: these guns could independently be trained and aimed. However, the shells were too heavy for safe handling and the V-class boat was too cumbersome for operations as an attack submarine. "Nautilus" was converted into a seaplane filling station and amphibious support ship for World War II.
 
 
 1931
Not to be outdone by the British or the Americans, France fielded "Surcouf" – 361 feet, 3,304 tons – the world's largest submarine until World War II. Armed with twin 8-inch guns and an airplane. "Surcouf" disappeared in 1942, probably after collision with a merchantman.
 
 
1932
U. S. Navy opened a competition for the development of a light-weight diesel engine, more suitable to submarines than any currently in production. While the number of engines which might be purchased for submarines was too small to justify the investment, there was a large commercial market waiting in the wings: the railroad.
 
1932
Japanese submarine designers moved out from under the shadow of the Germans, and, on their own, focused on three basic classes: the I-boats, most of them about the same size as the German U-cruisers; the RO coastal boats, about the same size as the German Type VII (see below) but not as capable; and the HA-series of midget submarines, in many variations.

The Japanese were more serious about submarine aircraft carriers than any other navy: they built their first, the 2,243 ton, 320-foot I-5, in 1932. It was equipped with one floatplane. In the next 12 years, they built 28 more, in ever-increasing sizes.
 
1932
The German government approved the clandestine construction of sixteen new U-boats.
 
1935
March 16, German Chancellor Adolph Hitler renounced the Treaty of Versailles. A few weeks later, the first of a new series, U-1, entered service.
 
 

1935
Captain Doenitz defined his fundamental concepts for the next conflict: "Tonnage War" and "Wolf Pack." The first replicated World War I experience – sink ships faster than they could be replaced, for a long enough period, and you could strangle an island nation like Britain.

The second – teams of seven or eight boats, attacking on the surface, at night; submerge to escape; re-surface and speed ahead to get in position for the next night's attack. The 15-knot surface speed of the U-boats was almost twice that of an average convoy, and equal to that of most anti-submarine escorts.

As with World War I, Germany developed several classes of U-boat: typical were the coastal boats (Type II), long range boats (Type IX), and jack-of-all-trades boats (Type VII), which became the mainstay of the fleet: more than 700 completed – in six variations, A through F – by the end of the war. Typical displacement (surface) about 760 tons, length 220 feet, range 8,700 miles with a functional endurance of seven or eight weeks without refueling. Dive time: 20 seconds to a maximum safe depth of 650 feet.

 


A Type VIIC U-boat – the mainstay of the German World War II submarine fleet – being welcomed on return from war patrol.
 
1938
An experimental 140-foot, 213 ton Japanese HA boat topped 21 knots – submerged. The Japanese also developed the world's most effective torpedo: the "Long Lance. " The MK95 submarine version had a 900 pound warhead, wakeless oxygen-fueled turbine, range five miles at 49 knots. Contemporary U. S. Navy torpedoes had half the warhead and half the range – when they were working. See below.
 
1939
While on sea trials, the brand-new
U. S. Navy SS-192 "Squalus" sank in 240 feet of water; an incompletely-closed valve caused flooding in the engine room. Twenty-six men were killed in the flooded section; there were thirty-three survivors. All were safely brought to the surface in four round-trips of the McCann submarine rescue chamber.

"Squalus" was salvaged, renamed "Sailfish," and served to the end of World War II.
 

Salvage operations above "Squalus," with two heavy-lift pontoons about to be sunk and lashed to the hull.
 

1939
Ten days after the "Squalus" disaster, a junior officer opened the inner door of a flooded torpedo tube and inadvertently sank the British submarine "Thetis." A few men got out through an escape hatch; ninety-nine were lost.

The British developed an on-board escape system, whereby sailors waiting their turn to go out through a pressure-modulated airlock (and chest-deep in water) would be able to breath through individual oxygen masks, permanently stored in the fore and aft torpedo rooms.

The British also developed positive interlocks to prevent a recurrence, salvaged the boat and put it back in service, renamed "Thunderbolt." She was lost in combat in 1943.

 

1939
At the beginning of the year, Hitler told Doenitz that he was planning for a war six years in the future; accordingly, Doenitz developed plans for the construction of a U-boat fleet of 300 Type VII boats. This would allow 100 on station, 100 in transit and 100 in training or under repair. However, Germany moved into Czechoslovakia in March and Poland in September. On the 3rd, the British issued an ultimatum: get out of Poland. You have two hours to make up your mind. The Germans did not respond. World War II began.

Germany then had 57 U-boats in service, only 38 of which could be considered "sea-going." For the time being, it would be enough.

 

1939
The U-boat war started under "prize rules." But not for long. On the first day, U-30 sank the liner "Athenia" without warning; 122 of 1,100 passengers were killed, including 28 Americans. To their credit, the German High Command was stunned, although they tried to pretend that the sinking was caused by a time bomb planted by the British to inflame public opinion against Germany. As late as January 1940, Minister of Propaganda Joseph Goebbels was ordering his staff "to continue running the "Athenia" propaganda . . . bearing in mind the fundamental principle of all propaganda, i.e. the repetition of effective arguments." The German public did not learn the true story until after the war.

Toward the end of September, the High Command authorized "seizure or sinking without exception" for merchant ships trying to radio for help when ordered to stop. A week later, U-boats were instructed to sink without warning any ship sailing without lights. The commanders were instructed to enter a note in the log that the sinking was "due to possible confusion with a warship or auxiliary cruiser."

By November, all pretense had been withdrawn with Standing Order No. 154: "Rescue no one and take no one aboard . . . Care only for your own boat and strive to achieve the next success as soon as possible! We must be hard in this war."

 
1939
Dr. Ross Gunn of the U. S. Naval Research Laboratory suggested that "fission chambers" using an isotope of uranium, U-235, could be used to power submarines. In a "Saturday Evening Post" article a year later, a science writer noted that one pound of U-235 has the equivalent energy of 5 million pounds of coal: "A five pound lump of only 10 to 50 percent purity would be sufficient to drive ocean liners and submarines back and forth across the seven seas without refueling for months."
 

1940
German scientist Helmuth Walter demonstrated a prototype for the first true submarine – a boat which in theory could operate submerged for an indefinite period, unlimited by battery capacity or the need for atmospheric oxygen. V.80 was powered by the decomposition of highly-concentrated (95 percent) hydrogen peroxide, H2O2, known as Perhydrol. In essence: when the chemical breaks down, it releases superheated steam to drive a turbine, along with oxygen to support conventional combustion or for respiration by the crew.

The hull-shape of V.80 was optimized for submerged operations, and the boat indeed demonstrated exceptional speed – 28 knots submerged. It also demonstrated exceptionally high fuel consumption, 25 times that of a diesel engine, at exceptional cost. According to one source, one 6.5 hour trial run consumed $200,000 dollars worth of Perhydrol.

The design showed great promise. However, Hitler thought his war was won, and plans for the production of a series of Walter boats were put in limbo.

 

The 1943 experimental 250-ton Type Wa-201 Walter boat, U-792, which hit 25 knots, submerged, on sea trials.

 

Research continued. Perhaps eight, in several variations, 250 and 300 tons, were put into service, 1943-44

 

The Type Wa-201 Walter boat, U-793, here partially dismantled at the end of the war.
 

Collapsible hydrogen peroxide storage bags being removed from the 300-ton Type XVIIB Walter boat U-1407 after the war. With the type of storage outside th pressure hull, fuel could be consumed without appreciable change in trim – seawater simply replaced the depleted volume.
 
1940
U. S. Navy ran depth-charge tests against an operational submarine (for most of the test, moored underwater without crew). They found that 300 pounds of TNT was not very effective; the explosive charge was doubled to 600 pounds.
 
1940
In June, France signed an armistice with Germany, and soon three French bases gave U-boats more convenient access to the open ocean. The eighteen months between July 1940 and December 1941 were known, to the German submarine force, as "the happy time." The score seemed limited only by endurance and weapons loading.
 
1940
U-boat operations were directed by long-range radio from fleet headquarters in Germany. The Germans assumed that the traffic would be intercepted, but didn't care, they were encoding all messages. However, even coded intercepts were useful; many individual boats could be identified by their unique radio signature. Even if a firm position could not be established, an analyst could determine when a boat should be headed home along one of several reasonably predictable routes.
 
1940
Italy joined Germany in June, bringing 105 submarines to the Mediterranean theater. They do not seem to have had much impact.
 

1940
In ramping up in anticipation of war – or, put more delicately, considering the at-the-time overwhelming public support for continued neutrality, as a "just in case" prudent measure – U. S. submarine production jumped from six or seven a year through the mid-1930s to seventy-one for FY1941.

The Navy settled on SS-212, "Gato," laid down in October, 1940, as the template: 312 feet, 1,825 tons, range 11,400 miles, 24 torpedoes. Over time, improvements were made including a thicker pressure hull beginning with the otherwise more or less identical SS-285, "Balao."

 

A typical World War II U.S. submarine, the "thick skin" SS-364, "Hammerhead." Wisconsin's Manitowoc Shipyard developed this sideways technique to accommodate launching a boat into a narrow river.
 
1940
On August 17th, Hitler formally declared a total blockade of the British Isles. Desperate to acquire more escorts, British Prime Minster Winston Churchill struck a deal with U. S. President Franklin D. Roosevelt: a loan of 50 over-age World War I American destroyers in exchange for long-term leases for base facilities in Newfoundland, Bermuda, British Guiana, and the West Indies.
 

1940
The first Wolf Pack went into operation in September. Where, in World War I, the simple fact of "convoy" kept the U-boats at bay, the Wolf Pack tactic (attack at night, rush ahead to the next rendezvous) set up a series of long-running battles. Early in the war, escorts were lacking and escort coordination was minimal. Often, they had not even talked with each other – let alone trained together – before meeting up in mid-ocean.

One example: On October 16, one U-boat spotted a convoy of 35 ships and called in the rest of his pack, six more boats. Another joined the next day. After three days, 17 of those ships had been sunk, two other convoys had been intercepted and 21 more ships sunk, without a single U-boat loss. The score would have been higher, but most of the submarines had fired all of their torpedoes and had to go home to re-load.

 

1940
At the end of the year, a German Naval Staff study noted the "accomplishments" of the U-boats, but called for the building of more battleships, taking shipyard resources away from submarine construction. At the time, a handful of operational U-boats (often, not more than ten at a time) were sinking twice as many ships at the surface fleet

To enhance morale – among civilians and sailors alike – a book of fiction and a feature movie showed Wilhelm Bauer battling bureaucracy and professional intransigence to reach the forefront of heroes: "Corporal Wilhelm Bauer, the first man who dove into the twilight." See 1850, above.

 

1940
By December, newly-perfected aircraft-mounted radar could pick up a surface-running U–boat at seven miles. Not a great distance, but farther than the eye could see at night. It was a start.

 
1941
America's role as a "neutral" was somewhat fuzzy: there was a steady stream of supplies flowing by convoy across the Atlantic, and for much of the journey, protected by U. S. Navy resources. After several U-boat attacks – sinking an American merchantman in May and a U. S. destroyer on October 30, with the loss of 115 sailors -- public opinion (which had been about 70 percent in favor of continued neutrality) began to shift.
 
1941
The code-breaking effort dubbed "Ultra" cracked the German Navy code; beginning in June – and, depending on whether new codes had been implemented -- the Allies could read much of the U-boat radio traffic off-and-on throughout the rest of the war.
 
1941
In August, U-570 became the first – the only – submarine ever captured by an aircraft; under attack, she was forced to the surface and surrendered. An escort ship soon arrived and took over. U-570 was thus transferred to the Royal navy, where, re-designated as "Graph," she served until being wrecked off the west coast of Scotland in March, 1944.
 
1941
In August, Adolph Hitler demonstrated a constitutional inability to keep hands off and let his commanders run the war. Against all advice, in a misguided effort to protect his supply lines to North Africa, he ordered a shift of submarines from the Atlantic to the Mediterranean. (Misguided? How, indeed, could a submarine protect a surface ship against the principal threat, which was air attack?) This soon led to an order to a shift of all operational boats from the Atlantic theater – at a time when there were Atlantic targets aplenty, and good weather in which to enjoy them. The "Happy Time" soon came to an end.
 

1941
Japan attacked the American naval base at Pearl Harbor, Hawaii, on December 7. There were 25 I-boats assigned on station around the islands. They did not see any American warships. Five HA-midgets attempted to penetrate the harbor before the air attack began; they achieved nothing but their own destruction. One became the first casualty of the Pacific war, sunk by the destroyer "Ward" as a unauthorized interloper in the offshore defensive sea area – before the air attack had begun. The destroyer sent a flash message to headquarters; headquarters thought it might be a false alarm.

The battle fleet was seriously damaged, but in time all ships were back in service except for two obsolete battleships: "Arizona," sunk at her mornings, and "Oklahoma," which sank while under tow back to the west coast for repairs.

The major effects of the attack: to coalesce American public opinion as never before, and to force the U. S. Navy to abandon an ingrained fascination with battleships and shift the burden to the new-generation warships, the aircraft carrier and the submarine.

At that time, the U. S. Navy had 111 submarines in commission – 60 in the Atlantic, 51 in the Pacific. Many were barely capable. "Gato" was commissioned at the end of the month; it would be several years before a fully-capable submarine force was in place.

With the approval of President Franklin D. Roosevelt, the U. S. Navy implemented unrestricted submarine warfare that same day. To salve the conscience of those who had for so long deplored German practice, all Japanese shipping was defined as being in the service of the military, and thus need not be considered as "merchant vessels."

 

Submarine pioneer Admiral Chester Nimitz assumed command of the U. S. Pacific Fleet on December 31, 1941 – on board the only available undamaged warship, the submarine "Grayling." The aircraft carriers were at sea.
 

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February 18, 2006