"The Earth is Round
British Admiralty - Operations Division
Research Section - Submarines - 1946
Imperial Japanese Navy Distant Operations
Operation Oni 3
The Japanese attack on the Panama Canal was one of the most daring operations of the war. It can be compared to the attack on Saint-Nazaire (Operation Chariot) in terms of pure audacity. It was the only operation of the submarines of the Imperial Japanese Navy that had a real strategic impact, as it seriously damaged the Allied shipping organization. However, this effect was only felt for six months, so its moral impact can be considered more important.
Planning: March-April 1942
The initial plan for this operation originated in an unusual meeting of the Sixth Fleet staff meeting in March 1942 to consider ways to enhance the prestige of the submarine forces. One cannot escape a strange feeling of vagueness when examining this plan, especially if one refers to the rules in use in the Royal Navy regarding the planning of operations. In fact, this operation with major strategic ramifications was planned without any particular involvement of the Combined Fleet staff, except for an initial approval! At the time, the Royal Navy and the US Navy were convinced that the two distant operations conducted in the same week by the submarines of the Imperial Navy were part of an extraordinarily well orchestrated plan. In reality, nothing was coordinated and the planning teams of the two operations were independent. The exact date of operation Oni 3 (Panama) was left to the discretion of CV Takamura, commander of the submarine fleet, who could have accelerated the execution of the operation by a day or two, or on the contrary to delay it, for example to wait for a favorable weather. Conversely, at the departure from their bases, the route plan of the four submarines of the Oni 2 operation (New York and Norfolk and Norfolk - see August 25th) foresaw that they could attack on the 25th, and the fact that the attack actually took place during the night of the 24th to the 25th is a tribute to the qualities and punctuality of the Japanese crews - but here again, the commander could have decided, depending on the situation, to follow a slightly shorter or a little shorter or a little longer, or even to wait for a favorable moment in front of their targets. In theory, the two operations could even have taken place at the same time, but only an improbable chance would have been responsible for it, not a learned planning!
This inaccuracy is due to the semi-feudal nature of the Imperial Navy's staffs. Admirals commanding the fleets of the Imperial Navy Fleet could mount on their own initiative, and to a degree inconceivable to the Allies, operations of a certain magnitude. It is a fact that Vice Admiral Komatsu obtained the approval of Admiral Yamamoto for the Oni 3 operation, but also that it was never discussed at a higher level. Thus, one of the most daring strategic attacks of the war was conceived and implemented as a banal tactical operation of a submarine fleet.
The first version of the plan for this operation, reproduced below, was found on documents seized in Singapore during its recapture. It should be noted that it is only a draft, not much more elaborate than an initial outline, and in fact, the action finally carried out differs in many respects, starting with the date, but no other document on planning has been found to date. The US Navy was particularly meticulous in excavating the ruins of the Sixth Fleet headquarters at Saipan, but the almost complete destruction of the place has unfortunately not allowed to find any information.
"Operation Oni 3
The submarine cruiser I-10 (type A1) will be detached from the 8th Submarine Squadron. It will take command of a group composed of five submarine cruisers from the 1st and 8th Squadrons (I-17, 21, 25, 27 and 29, all type B1). The group will gather at Kwajalein. Each ship will carry in its seaplane hangar a fast twin-screw speedboat of 8.5 meters. It will also take along 14 members of the Navy commandos who will have undergone special training in explosive demolition. Two of the boats will carry only 10 men, the space freed up being occupied by 500 kg loads of explosives.
The boats will be fully prepared and the men will climb into them inside the hangars; then the boats will be rolled on their cradle to the catapult and undocked at the moment the submarines dive. At 30 knots, the estimated time to the target is about 20 to 25 minutes. The Navy commandos will be armed with machine guns, grenades and explosives. They will be dressed in their uniforms, dyed to resemble those of the US Army, at least at night. The boats will be marked in English words, which will fly the American flag until they reach land. A few men fluent in U.S. English will be part of the attack force, in order to respond to any questioning in a sufficiently convincing manner. [Note - Amazing amateurism: the Japanese wanted to pass off their boats as fishing boats; however, the local boats were flying the Panamanian flag and their crewmen spoke Spanish and little or no English, a stop would have ended in disaster].
These special forces will attack and destroy the Miraflores locks on the Panama Canal. There are four locks (two pairs of successive locks placed side by side), for a total of six gates. [Note - Brief and inaccurate description]! The locks are located 8 km from the entrance of the canal. The whole complex they form is about one km long, and small boats can disembark troops on either bank a few dozen meters from the first locks. The doors of these locks are about two meters thick. The two downstream gates can be destroyed by heavy charges of explosives brought by the boats, the four others by blowing up their hinges with charges placed by the commandos. The weight of the water will do the rest, including emptying the lake of Miraflores. If this operation succeeds, the Panama Canal will be closed for at least a year.
Two submarines will be waiting at an offshore rendezvous point to pick up the members of the commandos. The other four will stand guard to intercept any enemy vessel heading for the rendezvous point. The special forces men who could not reach this point will go to the rendezvous point will head for the neighboring neutral countries, from where they will be able to reach Peru, where a large Japanese community resides. They will then be repatriated by submarine.
No activity of our submarines has yet taken place on the West Coast of the United States.
No other operation of the Imperial Navy will take place in these waters before this one, in order to give the enemy a false sense of security. [Note - The Sixth Fleet left the West Coast of the United States alone from March to August 1942, because of the preparation of this operation. Its easternmost attacks (as seen from Japan) were conducted in the vicinity of theHawaiian Islands].
This attack was planned for September 1942."
[Note - Some fragmentary indications have been found that the Navy sought, but did not succeed, in attacking the Gatun Locks and emptying the main lake supplying the canal with water].
Preparation: May-July 1942
During the months of May and June, the Transport Force trained and rehearsed all aspects of the operation. When the preparation of the operation began, the Imperial Navy knew that its codes, including the most secret ones, were in danger of being deciphered by the Allies. The security around the operation was particularly tight, and few people outside of Kwajalein knew about it. The cover story chosen was credible in its simplicity and the Imperial Navy would use submarines equipped with hangars to serve as mobile bases for its special forces in raids against enemy installations in the Pacific Islands. One of the consequences of these draconian security measures was that even for the Imperial Navy High Command, apart from Admiral Yamamoto himself, the announcement of the success of the operation was a huge surprise.
Getting the submarines was no problem, nor was converting them. The regrouping took place at Kwajalein in early May 1942. The I-21 had purge problems during one of the first tests and dived uncontrollably to the bottom of the lagoon. Although there was damage, the ship would have been lost in deeper water.
One of the main difficulties was not expected: how to train the members of the commandos to operate from a submarine? It had never been done before and the soldiers had no idea how to keep themselves in good physical condition or even how to keep their gear and weapons in good condition in the damp and cramped corridors of a submarine. According to witnesses found in the Marianas, CV Takamura paid his own way to encourage the commandos, happy at the prospect of giving their lives, but reluctant to spend weeks cruising in a submarine. Takamura repeated like a slogan: "The Panama Canal is the navel of America, the navel of the power of the United States!" [Note - The word used for "navel" evokes in Japanese the point considered particularly vulnerable where the blade slides in during seppuku.]
The initial plan called for the use of 8.50 meter fast boats, with two propellers, carrying 14 men, in the hangar of each submarine. These boats were replaced by the combination of two fishing boats, one of 9 meters and another of 7,50 meters, both of which could be housed in the seaplane hangar of each submarine, the smaller one fixed on the larger one during the transit. These boats, built in the Marianas, were very similar to those of the South American fishermen. Their reputation of solidity was well-founded. They used homemade outboard motors that were extremely common in all the tropical seas (where they are generally old car or truck engines with a crankshaft is extended by a shaft carrying a propeller). The engine was fixed at the back of the boat on an articulated support allowing a sufficient clearance with the horizontal. To extract these boats from the seaplane hangar of the submarine, the smallest was hoisted sufficiently high, the larger one put on the catapult, taken out of the hangar thanks to the rails of this one and put on the bridge at a good distance. The process was repeated for the smaller boat. Once the commandos were on board, the submarine simply dived under the boats.
The possibility to embark two boats allowed to increase significantly the number of special forces participating in the operation. Each boat was manned by four men, three sailors and an officer. Each submarine was thus able to deploy 30 men, bringing the total landing force to 180 soldiers (plus 48 sailors). The necessary space was found by removing the reloading torpedoes and by removing all the equipment intended for the use of the seaplane and useless for that of the boats.
To use a massive load of 500 kg to blow up the lower doors was a simple idea, but such a load was difficult to transport. In the spirit of Japanese combat sports, it was decided to use the energy of the water mass in the lock. The only thing to do was to weaken the gates and let the water do the work of destruction as it flowed through.
But there were two locks: the southwest lock was primarily for military traffic, the northeast lock was generally used by civilian traffic. And each lock had five gates, each with two wings. The minimum objective was therefore to destroy, or at least severely damage, the lower and intermediate gates, blocking the gates to the lake in their open position and to demolish the control and command equipment of the locks.
Approach: July 20th-August 21st 1942
The Transport Force left Kwajalein on July 20th and proceeded quite slowly to its destination. It arrived off Panama a month later without being detected, having chosen an extremely unfrequented route. The radio silence was absolute, the commanders of the six submarines had even locked up the Morse code manipulators. The headquarters of the Sixth Fleet knew it would not have any information until days after the attack.
Another major dilemma was the choice of approach. The safest and least likely to be subject to U.S. aerial reconnaissance was 100 miles long after passing Punta Mala, more or less following the coast, but the bottom was shallow most of the time along this route. The solution chosen was an individual approach to Punta Mala by each submarine for the landing, then the formation of a real train on the surface, the six submarines at intervals of one kilometer. We assumed that anyone reporting the vision of six large submarines making their way to Panama City on the surface, in tail, would be considered drunk or a victim of hallucinations...
At 30 miles from the objective, the six submarines would continue, submerged, therefore at low speed, by day, then on the surface, by night, grouped together, to reach in time the position chosen off an uninhabited place of the coast. Three submarines would recover the members of the commandos, the others seeking to attract attention away from the rendezvous point. After the attack, a large number of false periscopes were to be disseminated to deceive the enemy. A simple mechanism allowed them to emerge slowly, to stay a quarter of an hour on the surface, and then disappear for 50 minutes, the process repeating itself in theory for 24 hours before they sink definitively; a white cloth simulating a "feather" was even attached to it to give an impression of movement. In spite of all these precautions, significant losses were expected.
The approach of the "submarine train" during the night of 21-22 August was probably observed by a good number of small boats, and probably even by a brightly lit freighter, presumed to be neutral. However, no alarm was given and the submarines dived quietly in the early hours of August 22nd, 1942. The month of August being in the middle of the rainy season (May to November), visibility was poor in most of the Gulf of Panama, with frequent squalls, thick clouds and numerous thunderstorms. It is quite possible that the submarines of the Imperial Navy could not be clearly identified by anyone. Their crews were pleased to see that many small fishing boats were sailing in the area, carrying many lanterns. The use of acetylene lamps to attract fish and squid was widespread; it had been planned and lamps of this type had been taken along for the boats intended to land the commandos.
In sight of the objective: August 22nd, 1942
The submarines surfaced on the 22nd, at night, still in limited visibility with a low ceiling and showers. The wind was only blowing at six knots. Each submarine took out its two boats as if on exercise. The commando members boarded, the engines were started, and the submarines dived slowly. The four "fishermen" of each boat had remained standing on the deck of the submarine to prevent their boats from banging against the catapult rails as the dive began.
As soon as the boats were afloat, they climbed in. The flotilla got into running order and took advantage of a small rain squall to make rapid progress along the coast towards the canal. The coastline was normally well lit, but the beacon lights were obscured.
Sizeable american troops were present in the Canal Zone (42,000 men), but as the months went by, it seemed that the Imperial Navy had no intention of approaching it. The rigorous discipline and vigilance of the early days of the war had inevitably given way to a more relaxed attitude, approaching to the routine of peacetime. Moreover, the main threat expected was an air attack from aircraft carriers, possibly preceding a full-scale landing.
The chain of command was effective, but focused on this type of threat. An important anti-aircraft radar warning network had been built, air patrols organized in the Gulf of Panama and fighter aircraft based on newly built airfields. Powerful coastal batteries had been installed, but while their heavy guns were on alert every night, the small-caliber flak stations were not, their servants being present only during the day. The US Navy had old submarines in Panama (S class) for coastal defence (on the Atlantic side, some old French Navy vessels were used for anti-submarine warfare training).
Finally, the maritime patrols in the Gulf were constant, carried out by the destroyers of the 15th Naval District, reinforced by smaller vessels. A dozen patrol boats and minesweepers ensured the surveillance of the area. Two of them, the minesweeper Catbird (AMS-68, 350 tons, a converted trawler) and the coastal minesweeper Magpie (AMS-2, also a converted trawler), were at sea on the night of 22-23rd August 1942.
Each ship crossing the Canal was required to carry a platoon of armed guards, ready to intervene in case of unexpected maneuvers or behaviors, such as the dropping of a time bomb or a mine during the crossing of the locks. The locks were patrolled to prevent any risk of sabotage by small groups of individuals. The total force guarding the locks was of the order of several infantry sections, but there were no permanently manned fixed defense posts or organized entrenchments. Networks of barbed wire had been put in place and trenches dug in the muddy terrain, but the rain made these difficult to use and were being replaced by concrete shelters, more for anti-aircraft purposes.That evening, most of them were partially or totally flooded, as the rain had been particularly heavy the day before.
The American provisions were well known to the Japanese. The first protection measures had been taken long before the war, and gradually strengthened as tension with Japan increased. Japanese naval intelligence officers, mingling the crews of the merchant ships transiting through the Canal, had been able to observe them at leisure. After the beginning of the war, information transiting through the Japanese embassy in Peru had still been provided by Japanese sailors serving under false identities on neutral ships. But the main source of information was represented by the weekly reports sent by the spy Akiyama and transiting through neutral embassies (the Spanish embassy until October 1942). It is on the basis of this information that the approach route and the landing point were chosen.
Akiyama also gave very precise information on the situation of most of the defense posts, as well as on the habits of the naval patrols.
The main problem was the 8 km of water to cross from the entrance of the Canal to the locks of Miraflores. The Canal was only 300 meters wide at most and its banks were dotted with artillery batteries and searchlight positions (for flak, but also to light the Canal), which had a direct view of the narrow passage. Escaping detection was obviously impossible. The only solution was to pretend to be Panamanian fishing boats, many of whom defied the American prohibitions to fish in waters, which are rich in fish due to the abundance of organic waste thrown up by the ships that passed (in July, some 50 night-time violations of the prohibited zone were noted). This is why six of the twelve Japanese boats lit their fires before they reached the approaches to the canal. They proceeded at a reduced pace, with the members of the commando hidden under tarpaulins, themselves camouflaged by nets. It was a long and uncomfortable journey, but it was made in the midst of groups of other boats, just as well lit.
Attack: August 23rd, 1942
At 00:30 on August 23rd, the flotilla entered the first segment of the canal, before the Miraflores locks. Theoretically, there was still 30 minutes to go at moderate speed.
At this moment, luck, which had already served the Japanese well, could have abandoned them: the boats were spotted by the hydrophones of the minefield installed south of the entrance of the Canal. However, as the Japanese knew, the signals from these hydrophones were generally neglected. The reaction of the hydrophone operators to propeller noises reminiscent of fishing boats was usually to conclude that they were still unruly fishing boats. This was the case that evening and the mines were not set off.
The first two boats docked at 01:50 on a small beach downstream of the locks, on the eastern shore. The commandos quickly disembarked, dressed in dark gray silk uniforms.
Some had the mission of killing the guards with weapons equipped with silencers. They were accompanied by specialists in charge of clearing a path through barbed wire or other obstacles. The first guards were taken by surprise, where they were seeking to take shelter from the torrential rain. Their tour of duty having begun at midnight, the trucks that had brought them had long since left.
Nevertheless, if the surprise allowed the attackers to put their charges on the downstream gates of the two locks and the next gate of the east lock, it could not last forever.
The Americans reacted at first, as one can imagine, in great confusion. One of the guard posts succumbed after informing the command post that it was under attack by German soldiers! But the alert was given. As soon as their presence was visibly spotted the Japanese began firing light mortars at the locations of the American troop concentrations (located thanks to Akiyama's reports). They also began to open fire on anything that came their way, destroying "mules" (the small electric locomotives that pull ships through the lock) and set fire to the administrative buildings and the lock control tower.
On the west side (the military side), the two downstream gates (four wings) could be destroyed, but then the Japanese moved up the lock into an area battered by two machine gun posts (one .30 and one .50). These two posts had been set up at this location unbeknownst to Akiyama, along with a barrage balloon unit which, had been well reported... The area was devoid of any building that could be used as a cover and represented a perfect field of fire for the machine-gunners who were now wide awake !
The Japanese had no chance of getting through, although about twenty men had sacrificed themselves in vain at this point.
On the east side, the attackers succeeded in destroying or irreparably damaging seven of the ten lock gates, including the two on the upstream gate. This destruction should have been enough to destroy the lock completely, even to empty the lake of Miraflores, and it is what that the commandos hoped to achieve by taking off. The upstream gate was badly damaged and what was left of it was blocked in the open position, the hinges bent. The intermediate doors were weakened enough that the thrust of the enormous mass of water would eventually tear them off and smash through the downstream doors, which were already badly damaged. But the Americans had planned a last safety measure: the rush of water through the lock caused the automatic release of an emergency dam so secret that even the omniscient Akiyama had not heard of it. The water flow was reduced by 90% and what remained of the intermediate gates held. The level of the lake was not expected to change significantly before the repairs.
When the Japanese began to stall, however, they were confident that they had more than half succeeded in their mission: one lock badly damaged, the other destroyed, and Lake Miraflores being emptied... They had already paid a bloody price for this exploit. On the 180 Japanese soldiers engaged, about thirty had been killed. Thirty others, in charge of the operation north of the locks, did not receive the recall signal in time and were trapped. Twenty-two fought to the last breath, as it took the American garrison four days to defeat them. No prisoners could be taken, as the Japanese special forces, all fanatical, preferred to fight to the death, even without hope. The last eight managed to escape south on a stolen fishing boat and reached Peru, where they were interned by the Peruvian government under pressure from the United States. Two of them managed to escape and reach Japan.
The remaining 120 soldiers, including about 20 wounded, managed to reach the ships.
But if the landing point was judicious for the attack, it was much less so for the retreat. If the American gun posts on the banks of the canal had been properly informed of what was happening, no boat could have escaped. But in the confusion, darkness, and an ever-present rain, the American response was erratic at best.
Eight of the twelve boats made it through, the other four succumbed to fire of all calibers, which also swept away several small Panamanian fishing boats, very badly punished for having wanted to make a miraculous fishing on a bad night...
The withdrawal to the sea was a little easier. At 03:30, the I-21, I-25 and I-29 opened fire on Panama City with their 140 mm guns, which increased the panic among the defenders. The Japanese fire was inaccurate and caused only insignificant damage, but triggered a heavy fire from the shore batteries and the flak, whose posts had been activated shortly after the first explosions. The anti-aircraft guns set the sky on fire in an attempt to stop an air attack that was believed to be imminent, while the coastal batteries (including the huge 16-inch guns) tried in vain to reach the submarines, which took cover by diving. The unfortunate minesweeper Catbird, having seen one of the submarines firing, tried to catch up with it. But caught in a beam of searchlights, it was sunk by coastal artillery fire, while the submarine he pursued had just dived. Two fishing boats were also sunk by mistake. The diversion was successful, since nobody was interested in the I-10, I-17 and I-27 they picked up the commando boats in the opposite direction. In total, out of 228 men (180 soldiers and 48 sailors), 113 were recovered.
The submersibles dived towards the open sea. Once out of range of searchlights, they surfaced, to escape at full power until daybreak, dropping false periscopes as they passed. Some of these decoys were bombed by planes sent to search for the submarines, but most of them disappeared by themselves much sooner than expected.
Consequences: August 24, 1942-February 1943
The impact of this attack was immediate - but far less significant than the Japanese had hoped for. The importance of the route through the Mediterranean and Suez increased instantly. A significant number of ships had to be dedicated to the sole communications between the West Coast and the Pacific front, and the United States launched a major effort to increase their east-west rail capacity, work whose consequences had a lasting impact on the organization of American domestic transport.
Early Japanese estimates of the damage inflicted predicted that the Canal would have to remain closed for two years to rebuild the Miraflores locks. The critical part of the project was the reconstruction of the gates, which in theory required a full year year, plus two months for their delivery and installation and as much for the adjustments and fine-tuning. But the Japanese did not know that spare doors and all kinds of parts had already been manufactured and were stored on site! Moreover, as we have seen Miraflores Lake had not been drained.
In fact, only six weeks after the attack, the canal was back in service at 50% of its capacity. And by February 1943, the restoration was complete! The capacity of the canal was even greater than it was at the beginning. Indeed, the decision to build two Montana class battleships had been made in the meantime, the completion of a third lock, sized to accommodate these monsters, had been hastened. This lock was to be ready in the spring of 1945.
.........
The effect of Operation Oni 3 on Pacific operations was therefore relatively limited.
Nevertheless, the attack on Panama (followed, moreover, by the attack on the ports of the eastern seaboard of the United States) caused a lot of concern in the Allied camp and led to the mobilization of a large quantity of defensive resources of all kinds. But whatever its real impact on Allied capabilities, it is important to remember what President Roosevelt said when he announced to the American people the temporary shutdown of the canal: "The Japanese seem to have forgotten one thing: if the ships we build in our East Coast ports cannot pass through the Canal, that will not prevent them from going to attack them, because the earth is round..."
