August 25th, 1942
The submarines at the end of the world
British Admiralty - Operations Division
Research Section - Submarines - 1946
Imperial Japanese Navy Distant Operations
Operation Oni 2
One of the most remarkable aspects of the last war was the extraordinary variety and ambition of some of the operations of the Sixth Fleet of the Imperial Japanese Navy. This ambition can no doubt be traced to what Admiral Komatsu, commander of the Sixth Fleet, described (after the war) as a "disappointing" start to the war, in contrast with the success of the Allied submarines, about which the Japanese Admiralty did not fail to complain bitterly about.
Before the outbreak of hostilities, the Imperial Navy had an extremely wide range of submarines, which was characterized until the last days by a certain sense of the exceptional. Thus, the Japanese produced four enormous submarines of 6,500 tons (the STO type). These impressive vessels, larger than many pre-1914 cruisers, were originally conceived as submarine aircraft carriers (!), but finally used as underwater transports to islands cut off from any surface connection. The US Navy is currently testing two of them and the Royal Navy with the other two. Our common goal is to learn more about how maneuver very large submarines.
The Oni 2 operation, organized with the Kriegsmarine, used smaller but nevertheless respectable size, as well as pocket submarines, in charge of attacking what was, for the Japanese, the end of the world. The operation was conducted with inventiveness and a certain success. The translation of the initial plan of the operation drawn up by the Sixth Fleet is given below, the final plan having never been found.
Operation Oni 2 (7th Submarine Division)
"The four Junsen 1 (J1) type submarine cruisers are old (they were built between 1926 and 1929), but have a range of 24,000 miles. The A-type pocket submarines are now well known to the enemy since the attack on Singapore, which greatly diminishes their offensive value.
The three vessels of the 7th Submarine Division (I-1, I-2 and I-3) and the I-4 (of the 8th Division) will be modified to be able to carry each one a pocket submarine of type A or B pocket submarines on their decks, behind their 140 mm rear guns. They will take them to the East Coast of the United States, to attack enemy ports. The type B submarine, having a autonomy than those of type A, will attack the installations (shipyard, arsenal) of Norfolk (Virginia), the three type A units will attack the port of New York.
After having recovered the crews of the pocket submarines and, if possible, the pocket submarines themselves, the submarine cruisers will attack the local merchant traffic with torpedoes and gunfire, then proceed to Lorient, France, to be re-supplied with German torpedoes before returning to attack merchant ships off the East Coast of the United States, and then return to Japan.
Operation Oni 2 was intended to obtain a maximum surprise effect, using four pocket submarines before this type of weapon became too well known to the enemy. The psychological impact of this attack, on the enemy as well as on the Japanese people, will be extremely important, as well as the prestige that the Sixth Fleet and the entire Imperial Navy will gain from it."
Following the interrogation of Sixth Fleet personnel, it is clear that Oni 2 was part of a series of three one-time operations, with no planned follow-up: Oni (or Oni 1), in several phases, against the Australian merchant traffic, Oni 2, the attack on the east coast of the United States, and Oni 3, the famous raid against the Panama Canal. These operations were very disparate: Oni was much closer to Operation "C" (in which three of the four Oni 2 submarines participated) and operation "D", both of which were directed against the Allied shipping in the Indian Ocean, than adventures like Oni 2 and Oni 3. Although spectacular, Oni 2 had a very limited effect on the outcome of the conflict.
Preparations
The four ships were prepared at the Yokosuka naval base for what was to be the most distant attack mission ever carried out in the history of submarines at that date. The necessary modifications and training began in mid-May 1942.
Before the final departure, a stopover took place in Kendari to complete the gasoline fillings, correct some anomalies, and load the last supplies. It is there that the four pocket submarines were delivered by the Nisshin.
The submarines composing the squadron were:
- I-1, Lieutenant Commander Ankyu, carrying the HA-42 (type A)
- I-2, Lieutenant-Commander Inada, carrying the HA-38 (type A)
- I-3, Lieutenant Commander Tonozuka, carrying the HA-40 (type B)
- I-4, Lieutenant Commander Nakagawa, carrying the HA-35 (type A).
A 30-day leak test was ordered by the Sixth Fleet on the whole remaining stock of type 97 oxygen torpedoes, whose leakage problems had caused many failures and many accidents. The pocket submarines were armed with the torpedoes that passed the test, accepting the risks involved. This point is important, because these small 450 mm torpedoes, particularly powerful, had a range superior to the American 533 mm torpedo for a load that was at least equivalent.
The HA-40 pocket submarine was new and experimental. The pocket submarines of type A, from which it was derived, had been built in series. It had appeared that these machines lacked autonomy and had to be able to recharge their battery by their own means. The HA-40 was chosen as representative of this class to test the installation of a small diesel engine. It was equipped with a 40 horsepower generator and a fuel tank, all installed in a container fixed on the hull. This diesel had thus no mechanical link with the propulsion. It gave the HA-40 the possibility of recharging its batteries, even if it took between 16 and 18 hours, which translated into a range extended to 250 miles at 6 knots.
Unlike the operation against Singapore, it was planned that the submarine cruisers retrieve their pocket submarines on return from their attacks. This arrangement and the associated procedures, although simple, had a low probability of being successfully implemented. It represented more of a moral comfort to the crews of the pocket submarines than anything else. It appeared later, when reading the logbooks that the prospect of a mission without return did not frighten them.
The outward journey
The 7th Submarine Division left Kendari (Netherlands Indies) on June 30th, for a heroic 12,000-mile journey, which had to be covered in 55 days. It was planned to arrive near the targets on August 24th. Strict orders forbade them to approach any sea or air lines during their entire journey. The only targets they would have been allowed to attack were a battleship or an aircraft carrier. Admiral Doenitz's staff had been informed of the mission of the Japanese submersibles by diplomatic mail, the radio silence being de rigueur for everything related to the operation. Because of the length of the journey, this slowness of the communications did not prevent the German submarines operating in the sector from being informed even before they left their ports on the French coast. They avoided the New York and Norfolk areas and concentrated on the Caribbean area during the week the Sixth Fleet ships were scheduled to operate. It should be added that the information transmitted to the Germans was incomplete: it only mentioned a mission to hunt down Allied ships off New York, for propaganda purposes, before reaching a port in occupied France for the exchange of goods which was supposed to be the main purpose of the trip.
On its journey to the East Coast of the United States, the 7th Division passed west of Australia, rounded the Cape of Good Hope far to the south, before heading up the mid-Atlantic. This route, far from all sea lanes, was still not easy. The Roaring Forties took their toll on the stomachs, most of the journey was made on the surface at less than 12 knots (the average speed on the route was 10 knots). During the whole trip, only three ships were seen, from a distance, and no aircraft.
A final meeting to finalize the details was held on board the I-1, far offshore, and the squadron arrived in the zone fixed for the departure of the pocket submarines on August 24th, exactly as planned! Enemy patrols were incessant, but the four ships, each operating on its own side, managed to get close enough to the coast to be able to wait, resting on the bottom, for nightfall. At that moment, after a brief surface run towards the coast intended to facilitate the task of the pocket submarines to the maximum, the drop was done without problem for all the units.
The main attack (night of 24-25 August 1942)
1 - New York
The HA-32, 38 and 42 were successfully launched around 22:30 at about 8 miles from the coast.
A few days earlier, before the attack on Panama, the area would have been partially illuminated and the Coney Island amusement park perfectly visible. But since the day before, all the lights were obscured. On the other hand, the traffic was still heavy in the pass, both in one direction and the other, saturating the magnetic detection loops. But the ASM patrols had been multiplied...
At 00:54, the HA-42, which had reached the proximity of the Brooklyn naval base, was seen and very quickly depth charged by several patrol boats, dropping 20 charges in all. The small submarine had just enough time to fire its torpedoes in the general direction of the harbour. Both of them reached civilian wharves, the explosion of the first one destroying some boats, the second one making only a huge hole in the planks of a pier. The pocket submarine, completely crushed, was brought to the surface two days later by a floating crane.
At 01:08, in the same area, the HA-35 also launched its torpedoes, probably towards one of the US Navy cruisers present. However, they did not manage to hit a target of any importance, while the base was literally jammed with warships. The first one hit a jetty, its explosion causing no damage. The second exploded when it hit the pier of a wharf, after passing under the 500-ton patrol boat PE-57 Eagle, whose age (she was built at Ford in 1919) made her probably the most harmless of all the warships present. The unfortunate little ship was blown apart, sinking in three pieces. All 60 crew members were on board and 24 were killed.
After these explosions, patrol boats carried out a violent depth charge attack and several ships began firing, causing significant damage and even some casualties on land.
No one knew at the time what had happened to the HA-35. In 1947, its severely damaged wreckage was discovered, barely emerging from the mud on the bottom. It is possible that the submarine crashed into one of the holes lining the riverbed and that its crew then blew it up.
At 01:13, the USS West Point (ex America, United States Line, 33,961 tons, with about 2,500 soldiers on board), which had left a few minutes earlier from the transatlantic dock, loaded with troops bound for the United Kingdom, was shaken by an explosion. The responsible, as it was later deduced, was the HA-38 (Ensign Nobu). This one, unable to guide itself on the lights of the coast, had not followed the planned attack trajectory, perhaps because of a gyro compass failure on the final approach to the southern tip of Manhattan Island. One of the two torpedoes hit the stern of the liner on the port side, distorting bulkheads and structures. A severe water ingress ensued, flooding the engine rooms on that side. In four minutes, the heel reached 10 degrees to port, but filling starboard compartments allowed to limit the list. The vessel was immediately taken in tow and brought back to the dock. Apart from a hundred injured (most of them were victims of fractures caused by the shaking of the ship), there was no loss of life. It is remarkable that there were no deaths, even in the port engine room, where most of the sailors had to flee before the water broke in. The repairs took a long time, as priority was given to the warships. Nevertheless, on August 25th, 1943, as if in defiance, the West Point left New York for England, loaded with soldiers. After the war, the liner was returned to civilian life.
.........
The fate of the HA-38 is unknown. Several patrol boats in the harbor reported having attacked a pocket submarine leaving the harbor that night. In any case, the HA-38 did not show up at the rendezvous point and its wreckage was never found. In 1950, the families of Ensign Nobu and his crewman came to hold a funeral ceremony on a ship off the coast of New York.
2 - Norfolk Naval Base
At 21:30, the HA-40 (Ensign Isoru) separated from the I-3 in the shallow waters of the mouth of the Chesapeake Bay. It still had to travel nearly 40 miles to reach the Norfolk Naval Base, far more than the pocket submarines attacking New York. The I-3 had tried to get closer and even enter the Bay, but after spending the day in barely 20 meters of water and having half discharged its batteries, the density of patrols (clearly increased since two days) had forced him to give up. Lieutenant Commander Tonozuka surfaced, jettisoned the HA-40 and headed out to the open sea at 18 knots, still on the surface. He hoped that, if he was seen, the sight of a large submarine moving away from the coast would not worry anyone. After an hour's stop on the surface to recharge his batteries at the rendezvous point opposite Virginia Beach, he dived to spend the next 24 hours quietly on the bottom.
Meanwhile, Isoru sailed on the surface at 12 knots toward its destination, its diesel generator running continuously to maintain its battery charge. That may seem foolhardy, but he knew that his small boat was almost invisible, except at close range, and even there, the lights of the coastline greatly diminished the night vision of the surveillance patrols. Isoru had studied the activities of small Confederate David-type torpedo carriers in 1865 and had conducted numerous trials with pocket submarines in the Inland Sea of Japan. This had confirmed to him that these units were extremely difficult to discern at night and he had his submarine repainted in a very dark matte blue, instead of the standard glossy black - a deviation unthinkable in the Imperial Navy for anyone other than the officer commanding a pocket submarine, who had some latitude in view of the extremely dangerous nature of his missions. Isoru maneuvered his machine from the kiosk, where he had a flexible acoustic tube to pass on his orders to the quartermaster who accompanied him, as well as a gyro-compass repeater and a folding map holder.
The HA-40 passed Hampton Roads, whose anchorage was crowded with merchant ships.
Isoru stayed away from all the freighters in his path, never coming closer than within a thousand meters of them. His plan was modeled on the pocket submarine attack in Singapore - her navigation was easier, as the depths were deeper, the channels better marked, and the naval base much closer to the entrance of the harbour than was the Royal Navy HQ was at the mouth of Keppel Road. Nevertheless, around midnight, when he arrived between Fort Monroe and Norfolk with six miles to go to the naval base itself, her battery had only enough power left to travel 10 miles at 14 knots or 80 miles at 4 knots. Isoru then slowed his submarine to 6 knots, leaving only the diesel still running.
It took the HA-40 30 minutes to cover the next three miles, during which time the shoreline was far too close for Isoru to feel comfortable. In fact, he was seen many times, but was not bothered, being mistaken for an ordinary boat propelled by a slow diesel. Meanwhile, Isoru could engrave in his memory his escape route.
But at that moment, he came up against a real wall of patrolmen, set up the day before by the base command, not wishing to know the fate of those responsible for the Panama Canal security.
At 00:55, the little machine had not moved one meter forward, each time forced to turn around by a patrol boat. Isoru persisted, however, sailing at 4 knots, exposing the lens of his periscope only in periods of five or six seconds. It was then that luck favored him. A large ship was coming out of the base, surrounded by a court of escorts, but running straight towards the small HA-40!
The ship spotted was none other than the USS Alabama, a brand new battleship, launched on February 16th and officially commissioned on August 16th. The Alabama had returned to the shipyard to receive the missing guns of her K-turret and to carry out the usual small interventions after the sea trials. Once some of these were completed, a brief night out was scheduled to check that everything was in order. It was not a question of going out to sea, but of making a small tour in the Chesapeake Bay.
At 00:59, Isoru, blessing his ancestors whose protection had certainly given him this chance, launched his torpedoes at less than 400 meters, aiming at the bow, and hit twice. The first torpedo hit the battleship between the A and B turrets, the second hit it three seconds later at the height of the bulkhead separating the condensers from the forward engine room (N° 1). In both cases, the torpedoes went quite deep, crossing the anti-torpedo bulbs without difficulty (it is true that they were empty, whereas in normal times they would have been filled with water or fuel oil). The ordinary 450 mm torpedoes could not have overcome the protections, even empty, but the type 97 oxygen torpedoes had a very important explosive charge for a weapon of this calibre (350 kg of type 97 explosive).
The most serious was the fact that inside the ship, the watertightness between the compartments was not fully assured, due to the work in progress. The Alabama quickly heeled over, but was soon brought back to the naval base itself, especially since its machinery was intact.
Being in the middle of a naval base, the Alabama should have been easy to repair. However, the interior of the hull was still cluttered with junk, props, and all the other paraphernalia needed for the work, which blocked some of the watertight doors, preventing the pumps from being effective. Many doors and hatches were not yet sealed and not all bulkhead penetrations were sealed.
It was therefore with great difficulty that the battleship could finally be brought into a dock. The Alabama was finally put back into service in December 1942. In February 1943, she reached the Pacific through the Panama Canal, which had just been fully reactivated.
.........
The HA-40 escaped by diving. It apparently had very little hope of escape. The confusion in the base was Isoru's best ally, as well as the extraordinary luck which accompanied him in his navigation to the judgement.
At 03:30, after a few mishaps without consequences, such as the scraping of an anchor chain and three groundings, the submarine reached Hampton Roads, while the Americans were trying to sort out the mass of erroneous information sent by all the patrol boats. It then headed towards the exit of the bay at 4 knots, a speed that allowed it to travel another 50 nautical miles despite the exhaustion of its battery.
At 04:00, Isoru took out his periscope, checked that nothing was in his way, and noticed with pleasure that the fog had lifted. He took advantage of it to surface, or at least to emerge his kiosk, what allowed him to put back on his diesel to recharge his exhausted battery and ventilate the submarine. He thus advanced 6 nautical miles, until the noise of aircraft engines and marine diesels forced him to dive.
At dawn on the 25th, he put his submarine on the bottom, by 12 m of depth, and waited. He was 20 nautical miles from his rendezvous point. He spent the day waiting quietly, in absolute silence, listening to the noise of the engines of the patrol boats or of some freighters. At that time, the authorities at Norfolk base thought that the Alabama had hit large drifting mines anchored in the harbor. Isoru's approach had not been reported, and no torpedo trail had been observed.
An hour after nightfall, the HA-40 came up for periscope dipping and Isoru examined the surface. He was again able to raise his kiosk from the water and start his diesel. Surprisingly, he did not see any boats, except for a few fishing boats in the area, as he slowly made his way away from the coast off Virginia Beach.
On August 26th at 01:00, one hour ahead of schedule, the HA-40 reached the rendezvous point.
At 02:00, it dropped three small explosive charges. The I-3, which had left to recharge its batteries before returning slowly to land on the bottom, was rather surprised to hear them. It immediately surfaced less than a kilometer from the pocket submarine.
After a brief discussion, Tonozuka agreed to attempt one (and only one) operation to re-board the pocket submarine. As he later admitted, the risk involved was more than just unconsciousness, but obviously the gods were with him that night... Indeed, the pocket submarine was hoisted and secured on its rails without any problem at the first attempt, and the I-3 left the scene at full speed.
Secondary actions (26 August-10 September)
The 7th Japanese Submarine Division had one more trick up its sleeve, of no military interest, but very impressive for propaganda purposes. During the night of 27 to 28 August, the four ships shelled Atlantic City for half an hour. No target of any military value was there, and this attack had no impact on the American war effort. A hundred explosive shells hit the small town, famous for its casinos and gambling houses. About 50 people were killed and twice as many wounded, most of them caused by a single hit on a crowded restaurant. The explosions caused fairly large fires, with about 3% of the city's buildings, mostly built of wood, were burned.
.........
Then, the four submarine cruisers wanted to imitate the U-Boots of the Kriegsmarine and attack theallied shipping traffic off the coast of the United States. But they had presumed too much of their possibilities! From 26 August to 10 September, uncomfortable near the coast and in shallow waters, the four ships sank a total of four small freighters. On the 10th, the I-2 was surprised by a Catalina on ASW patrol. The old submarine tried to dive, but it took too long to reach safety and the seaplane's bombs gave it no chance. The three other submersibles reached France without playing the raider anymore. They arrived in Lorient on September 30th.
The political fallout
The impact of these attacks in the United States was of course considerable. Whether the one directed at New York had been a near-failure and that the attack on Norfolk was been technically easier than the one on Singapore, as the Royal Navy pointed out to the US Navy (but as the press never found out), did not change anything in the matter. Without doubt, the damage was limited to a small patrol boat destroyed, a troop transport out of service for a year and a battleship out of action for six months
But the magnitude of the press reaction made such rational analyses futile. The American public retained only that the national territory had been hit in its heart: New York itself, a symbolic city and one of the largest American naval bases. The attack on Atlantic City was a big cherry on top of this already huge cake and the wildest rumors began to circulate.
The anti-submarine warfare resources dedicated to the defense of the American coast were increased. Additional booms, nets, magnetic detectors, patrol boats and shore batteries were assigned to the defense of ports and some to the protection of civilian installations. These measures were not all wasted, as some of them were to hinder considerably the U-Boots...
.........
In Japan, Admiral Komatsu was over the moon. Ancient submarines, using a weapon that was about to be shelved, had been a resounding success. And it had been accomplished in the Atlantic, on the other side of the world... The prestige acquired by the Sixth Fleet even earned it compliments (a little forced) from the Army staff. It is true that the spectacular side of the operation provided the Japanese propaganda with a weapon of choice and that even the Imperial Army could not ignore it. Isoru was made a lieutenant on the spot, and the senior quartermaster who was the only other crew member of the HA-40 was promoted to ensign.
In Berlin, Hitler and the OKW rejoiced, at least in public: obviously, these Americans were not serious adversaries, and Japan would keep them busy long enough for the Wehrmacht to have plenty of time to finish off the Soviets. In private, however, Hitler expressed real dissatisfaction: without even asking permission, the Japanese had somehow stolen from them the media coverage of a theater of operations devolved to Germany. Moreover, Dœnitz complained (not without reason) that such a spectacular action would whip the Allies into a frenzy throughout the region and make it more difficult for the U-boots. Nevertheless, the end of German U-boot operations on the East Coast (which had begun on 11 January with Operation Paukenschlag / Drumbeat) was envisaged well before Oni 2.
The Japanese "gifts"
The 7th Submarine Division arrived in Lorient on 30 September 1942. There began the exchange of "gifts" - known as the "Yanagi mission" - which constituted the most discreet, but not the least important, reason for the Oni 2 operation. Three hundred tons of zinc ingots, which served as ballast for the submersibles, were unloaded, and replaced by an equivalent mass of lead free of traces of antimony and mercury in lead bottles. One hundred and fifty tons of other goods were unloaded, including 30 tons of rubber - a precious gift because the exploitation of the conquered plantations (in Malaysia in particular) was far from secured and Japan did not have too much rubber for its own needs. There had been question of sending quinine intended for the German troops who were fighting in Southern Europe, but all available quinine was at that time requisitioned for the troops who were assaulting Singapore. On the other hand, a Mitsubishi A6M2 fighter, in crates of course, was on the list of gifts carried by the I-1 (another one had suffered the same fate of the I-2). Indeed, the Imperial Navy hoped to dazzle the German airmen of which it had learned that they had difficulties to develop a carrier fighter worthy of the name. The Zero was from the outset the subject of a fierce battle for prestige between the Kriegsmarine and the Luftwaffe, which the latter won, in the name of its exclusivity of all that was flying under the Swastika...
It was the same for the light seaplane Yokosuka E14Y1 (Glen), brought, in boxes too, by the I-4. The seaplane was intended to be carried (all assembled!) by a Japanese "command" submarine, but the RLM was interested in it for the ASW fight.
The Kriegsmarine consoled itself with the most beautiful gift: the submarine HA-40, which had raised interest among German submariners. With the war against the USSR in full swing and the impossibility of sending ocean-going submarines to the Mediterranean or the Black Sea, the potential of this pocket submarine was considerable. The prospect of having it definitively at one's disposal to study at leisure and then duplicate this efficient, fast and proven weapon opened up unhoped-for perspectives...
It is known that the French Resistance and the RAF were responsible for the rapid elimination of a good number of these Japanese gifts.
An unexpected benefit
After such a long cruise, the buildings had to be refurbished. The work took two months, plus two weeks for testing and replenishment. The engines, of German origin (MAN), were completely overhauled, and above all, all the batteries of the electric motors were replaced.
The Germans had indeed been surprised by the completely outdated technology of the batteries used on both the large submarines and the pocket submarines, and asked many questions about the techniques and procedures used in the Imperial Navy in this matter. In reality, these batteries were very similar to those used by the Imperial Navy... of the Kaiser, during the First World War. A simple nd economical technology had its merits, but it only led to low-performance, short-lived products. Missing out on important improvements that could be made such as reinforced insulation between the lead plates or a 15 mm gap for deposit accumulation at the bottom of each cell, would have been a waste.
Noting that the batteries of the submarine cruisers were in poor condition (a very bad point for ships destined to strike far away), the Germans were not stingy with information and advice, going so far as to provide details on the design and manufacture of their own batteries. The Kriegsmarine embarked for Japan three Batterie-Experten (one per submarine), loaded with abundant technical documentation. The German experts did not idle during the trip, writing with the help of the specialists on board manuals for the maintenance of the Japanese batteries.
Without doubt, the Japanese industry was never able to produce the same batteries as the German industry, but it took advantage of the advice received, even without changing its outdated method of manufacture. The main improvements made were the following:
- use of better insulation to seal the batteries ;
- use of thicker lead plates, produced in double molds
- better control of the antimony content in the lead, reducing the production of hydrogen production and therefore the risk of explosions;
- provision of an 18 mm space at the bottom of the cells for the accumulation of deposits;
- reduction of the thickness of the glass walls of the batteries, allowing a significant increase in
The thickness of the glass walls of the batteries was reduced, allowing a significant increase in the volume of electrolyte and the use of thicker, and therefore more solid, wooden cases.
The consequences were a better capacity/weight ratio, as well as an improvement in the life and reliability of the Imperial Navy's batteries. From 1.5 kWh/kilo for 80 discharge-recharge cycles, they increased to about 4.4 kWh/kilo and 200 cycles. This progress, considerable for the Japanese, left them however still very far from the level reached by the batteries used by the Allies, which was 9 kWh/kilo for a minimum of 600 cycles. Nevertheless, this improvement was for the Imperial Navy the main benefit of the Oni 2 operation.
In October 1943, the procedures drafted by the German experts, barely adapted, were in use throughout the submarine force, and by August 1944, all submarines in operation were using the improved batteries. It was these batteries that allowed the Japanese submarines to be much more efficient and dangerous at the end of the war than at the beginning.
The German "gifts"
The three submarines carried a (relatively) large quantity of goods on their way out: this was the second part of the Yanagi mission. Among others, in each submarine were 200 marine chronometers, tubes and other electronic components, tons of plans, 250 magneto-acoustic mine actuators (in addition to those sent in March-April by train), some aircraft engines, plus 12 TMC (Torpedo Mine Type C), loaded in the rear torpedo compartments. Many of these goods were placed in watertight containers, arranged in a "trunk" fixed on the rear deck, where the pocket submarines had been on the outward journey.
The long way back
The submarines left Lorient on 17 December 1942 and headed south. Indeed, because of the high value of the goods being transported, it was decided not to tempt fate by returning to chase the transports on the American coast. But the luck that had accompanied them to New York and Norfolk was no longer with the three submarines.
Enigma messages were to keep the overly aggressive U-boots off their route - ironically, it was one of these messages that, deciphered by the British, put the HMS Sealion on the route of the I-4, which sank it with a torpedo in the Bay of Biscay, persuaded to have destroyed a large German supply submarine.
The I-1 and I-3 arrived in Yokosuka after two months of uninterrupted travel, on 15 February 1943. They were given a rapturous welcome.
The eight-month deployment quickly became legendary in the submarine world.
The 7th Division had gone to the ends of the earth, dealt a major blow to American morale and restored (symbolically at least) communications between Germany and Japan.
