On 1941 Dec 7, could Japan have targeted the Panama Canal instead of Pearl Harbor in a surprise attack?

Question

This question comes from a slightly related one.

At the time of WW2, most US industry was on the East Coast, including all of the shipbuilding for Carriers and Battleships. If the Panama Canal went down, it would greatly reduce the logistics of the US Navy in the Pacific.

So I want to know, did the Japanese Navy have the ability to destroy it in a surprise attack, let's say on 1941 Dec 7?

What I know so far:

• The Panama Canal has 6 water locks per lane. The locks have concrete walls but hollow steel gates, as per this documentary: https://www.youtube.com/watch?v=d-CaBIKTl4M , at 1:11:00 you can see they are a hollow frame. 1 bomb or torpedo will probably blow a hole in it, though it might not be enough to instantly drain the locks.

• Japanese Dive Bombers had the training, as evidenced by the many carrier hits they got in early WW2 (Coral Sea, Midway.) Note, I'm talking about hits, not necessarily kills. I reviewed those two battles and many times, the US Carriers got hit but survived (US Carriers seem a lot more stalwart than Japanese Carriers at that time). I'm only trying to point out that Japanese Dive Bombers seemed to have good training and accuracy.

• Edit: The Panama Canal Locks are powered by the Gatun Hydroelectric Dam. Maybe all you need to do is smash that dam, and the locks are suddenly worthless. I do not know for sure how long it takes to repair a hydroelectric dam, but it has to be on the order of months. From reading about bouncing bombs going after dams in Germany, they appear to be significant logistical targets.

• The Doolittle Raid (made by America) got 2 carriers, 4 cruisers, and 8 destroyers very close to Japan before being detected, and that was when they were already at war (1942 Apr 18).

• Japan actually designed and built some submarine aircraft carriers meant to raid the Panama Canal, so apparently they believed the Canal's defenses were not good enough to stop an aerial attack.

• The surprise attack on Pearl Harbor IRL was a total surprise, despite seeing airplanes on radar.

What I don't know:

• what AA defenses the Canal had at that time.

• what range and endurance a Japanese Naval Group had.

• possibly other things that make it impossible or unlikely.

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I'm trying to keep this specific so it doesn't get closed as too broad or too opinion based. I'm asking if the Japanese Navy had the ability. I'm not asking if it was a viable strategy or sound war plan.

Answer 1

So I want to know, did the Japanese Navy have the ability to destroy it in a surprise attack, let's say on 1941 Dec 7? I'm asking if the Japanese Navy had the ability. I'm not asking if it was a viable strategy or sound war plan.

Well, you're getting both. :) Evaluating it as a war plan is WAY more interesting.

Yes, but...

• It would be fixed in six months.
• Shipping can still go around South America.
• They'd have a hell of a time getting there.
• They'd have an even worse time getting back.
• They'd have to face the wrath of the intact US Pacific Fleet.
• They'd hand the US a golden opportunity to destroy the IJN piecemeal.
• All their fleet carriers are out of the first months of the war.

To keep this away from a "what if" answer, I'll lay out the problem in more detail in comparison to the already audacious Pearl Harbor attack, and its knock-on effects even if successful.

The Fleet

First, let's have a good look at the fleet which attacked Pearl Harbor. It wasn't just a few carriers, it was ALL their fleet carriers. And they needed a large support fleet of battleships, cruisers, destroyers, submarines, tankers, and supply vessels. This will become very important because of the range involved.

• 6 fleet carriers (all they had)
  • 409 ready aircraft + spares
• 2 Kongō class battleships (converted WWI battlecruisers)
• 2 Tone class heavy cruisers
• 1 Nagara class light cruiser
• 11 destroyers
• 30 fleet submarines
• 5 midget submarines
• 8 tankers (all impressed civilian ships)

The submarines were for long range scouting and screening. The destroyers for short range and anti-submarine work. Their surface protection was paltry against the US fleet.

Getting There

Tokyo to Pearl Harbor is about a 7500 nmi round trip... in a straight line. The Japanese took a circuitous route, avoiding shipping lanes, to avoid detection on the way out and back. All in all it took them 28 days.

Tokyo to Panama is twice the distance and twice the time. As we'll see it's likely 20,000 nmi to avoid detection and over two months in transit. Just getting there will be a serious challenge.

How Do You Get There Undetected?

Twice the time in transit means twice the chance of detection. It means twice the chance of someone screwing up and sending a radio message. It gets worse.

Let's start by looking at the shipping lanes at the time.

On their way to Pearl Harbor, the fleet took a northern route weathering rough winter seas to avoid major shipping lanes. They kept radio silence for two weeks and had a screen of thirty submarines.

But getting from Tokyo to Panama requires crossing sea lanes, there's no way around it. The fleet certainly won't risk traveling between Hawaii and the US West Coast. It must move through the island-dotted Central Pacific where it's at risk of being spotted by any number of merchant ships moving between the Americas and Asia.

I've estimated the distance using the Great Circle Distance going from Tokyo, Japan -> Majuro Atoll, Marshall Islands -> Pape'ete, French Polynesia -> Panama City, Panama at nearly 10,000 nmi one way. So 20,000 nmi round trip. Plus zig-zagging to avoid submarines on the return.

How Do You Fuel All That?

The vessels in that fleet have ranges from 5000 nmi (destroyers) to 10,000 nmi (some of the carriers, and both battleships) to 15,000 nmi (submarines). With a round trip of at least 20,000 nmi due to the Central Pacific route, that means refueling at sea. A lot.

Fortunately the IJN knew how to refuel even in heavy seas, something the US thought only they could do, but it's always a risky proposition. They did it for the Pearl Harbor attack, but to get to Panama means twice the number of refuelings, twice the risk, and twice the number of oilers.

And they had to do it all in radio silence lest they be detected.

Unfortunately Japan was so sorely pressed for oilers they impressed merchant ships for the role. All 8 tankers for the Pearl Harbor fleet were impressed merchant ships. To get to Panama they need to find 8 more or leave half the fleet at home.

Since the canal locks are a smaller target than the sprawling naval base and fleet at Pearl Harbor, it's possible they would leave half the fleet at home. Perhaps the two shorter ranged Zuihō class carriers making them available for other strikes at the start of the war.

The Attack

Our fleet has, somehow, safely arrived undetected and is now a few hundred miles from the Panama Canal. Now what?

The Defenders

The US was already well aware that the Canal was a target and had significantly beefed up their defenses, even against air attack... but it was incomplete on Dec 7th.

For defense against surface attack, the Canal was defended by heavy coastal defense batteries that would give a Kongō class battlecruiser a seriously hard time. So no surface attack was likely. As at Pearl Harbor, it would be from the air.

The Pacific end of the Canal had an SCR-271 radar set, the same at Pearl Harbor and the Philippines. While it successfully detected Japanese air attacks on Pearl Harbor and the Philippines, it was so poorly understood and poorly integrated into the air defense that the detection was ignored. There's no reason to believe it wouldn't also happen in Panama.

For air defense, Panama had 24 Pursuit planes, mostly P-36 Hawks and P-40 Warhawks. These are the same aircraft as Pearl Harbor, and both inferior to the Japanese Zero. As at Pearl Harbor, they'd probably get caught on the ground. They also had various anti-aircraft guns, definitely the 37mm Gun M1, but it was deemed inadequate.

Only two detectors were installed and in operation in the Panama Canal Department. The harbor defenses had less than one complete manning detail available. The anti-aircraft artillery had insufficient personnel to man the armament being installed in the Canal Zone and only enough ammunition for one minute of fire per gun for the 37-mm. guns. There were no barrage balloons.

There's no reason to believe the Panama Canal defenders would fare any better than Pearl Harbor.

The Damage: Six Months

With surprise, superior aircraft, and in larger quantity the Japanese would have total air superiority. With their large quantity of strike aircraft and skill at dive bombing it's a near certainty that both locks would be hit and disabled. They could even be torpedoed. The planners of the I-400 attack estimated this would put the locks out of operation for six months.

A team of three shipping engineers studied the documents and concluded that the locks at Miraflores on the Pacific side were the most vulnerable to aerial bombing, but the Gatun locks on the Atlantic side offered a chance of causing greater damage, since it would be harder to halt any outflow of water. They estimated the Canal would be unusable for at least six months following a successful attack on the locks.

But this doesn't cut off shipping between the East and West coasts. It does mean they have to go around South America adding thousands of miles and weeks to the trip.

This also doesn't cut off supply between the East and West coasts, the US has an extensive rail system to draw on.

What About Gatun Dam?

Or...

27 Million Tonnes of Earth and Concrete Doesn't Care About Your 800 kg bomb.

(Technically that's the entire dam, not just the concrete spillway dam... just forgive me this bit of hyperbole.)

Gatun Dam holds back the Chagres River creating Gatun Lake which ships transit going from the Atlantic to the Pacific. It's a very tempting target to do longer term damage to the canal. Could a Japanese carrier air strike breech the dam?

No. It's not like in the movies... unless that movie is Dambusters. Damaging a dam is really hard. Bombing a dam is even harder. Why? Looks easy. Just look at that huge target!

The problem is if you just drop a bomb on a hard surface, like the armor of a ship or a concrete dam or the ground, most of the explosion simply reflects into the air. The Allies found this much to their annoyance trying to damage the much smaller U-Boat Submarine Pens.

To do more than chip at it you have two options. First is to penetrate deeply before exploding. Then the force of the explosion is fully transmitted to the surrounding concrete. The Allies developed bombs like the 5400 kg, 6.4 meter long Tallboy. Cast from a single piece of high tensile steel, it had to be dropped from 5.5 km to allow it to reach terminal velocity and penetrate 5 m of concrete delivering 2400 kg of extremely potent Torpex explosive.

The Japanese had nothing like this in Dec 1941, nor could a carrier bomber carry it. The closest bomb they had was the 800 kg Number 80 designed to take out small bunkers. It was capable of penetrating 0.4 m of concrete, not even enough to bury the 2.8 m long bomb, and delivered 380 kg of Shimose Powder. A B5N torpedo bomber could carry one.

But a dam wall is practically vertical, so the bomb would hit it at a high angle and just skip off.

The second way is to press the bomb against the dam underwater and then explode it. Water is incompressible and so the explosive shock will translate to the concrete. The trick is to get it right up against the dam, otherwise that same incompressible water will shield the dam from the blast. This is why depth charges had a "kill range" measured in meters. This is further complicated by the presence of torpedo nets (I'm not 100% sure the dam was covered with torpedo nets, but the locks were) which will also stop a bomb or torpedo moving through the water towards the dam. WWII bombing techniques, even dive bombing stationary target, was not accurate enough.

This was solved, after much work, for Operation Chastise aka the Dambusters raid. It used a special spinning, bouncing depth charge called Upkeep that could skip across the water, hit the dam, roll down it, and explode at the bottom right up against the dam.

The Japanese had no such bomb, didn't have the aircraft to carry it, and didn't have the expertise to develop it. Upkeep weighed 4000 kg and delivered 3000 kg of Torpex. Japanese carrier based bombers were limited to 800kg. Japanese overlooked anti-submarine warfare, much to their great loss, and their depth charges stank. The available Type 1 Number 25 air dropped depth-charge carried just 140 kg of explosive.

...but a spillway gate might care about a few torpedoes.

Torpedoes were an option, if there were no torpedo nets. Not the dam itself, but the metal gates at the top used to control the water were vulnerable. During the Korean War, Hwacheon Dam was attacked by bombs and torpedoes disabling the gates.

This won't produce a catastrophic failure, but it will make the gates inoperable and might flood the lake causing additional problems and more things to fix.

Getting Home

The IJN kicked the hornet's nest. Now they need to get home.

If they're smart they refueled just before the attack, but now they're over 8000 nmi from home and will need to refuel at least once, probably twice, slowing them down and making them vulnerable.

After Pearl Harbor they left a shattered US Pacific fleet behind them, but still the US Navy searched. After Panama they have the intact and superior US Pacific fleet in front of them. And the US admirals are drooling at the opportunity they've been handed.

Tsushima Reversed

When faced with a fleet of roughly equal power to their own, a commander will try to attack it piecemeal. During WWI both Britain and Germany tried to trick the other into splitting their fleet so each piece could be overwhelmed. The Japanese, looking to repeat the success of Tsushima, had Kantai Kessen which would whittle the US fleet down with submarines and air attacks as it raced to defend the Philippines.

Now the Japanese navy had split itself. Its carriers, with an inadequate surface screen, were 8000 miles away from the rest of their fleet and busy kicking off the rest of the Pacific war. They'd be slowed by their merchant oilers and their need to conserve fuel for the long journey home. They'd been at sea for a month possibly needing repair.

The bulk of the US fleet would wait while US submarines, destroyers, and long range maritime patrol aircraft searched for the returning Japanese fleet. And the Japanese would have no choice but to run this gauntlet. Once found, it would be their turn to be whittled down.

The primary target for these attacks would be not the warships, but the oilers. So far away from home, the US knew they would need to refuel. Attacking the slow, vulnerable oilers would leave the Japanese fleet low on fuel. They'd have to slow, reduce their zig-zagging, and take a more direct and predictable route home giving the US more opportunities to attack. The US Pacific Fleet would serve to block their path.

Finally, with the Japanese fleet harried, damaged, low on fuel, and reduced, the intact US Pacific Fleet of 9 battleships, 20 cruisers, 3 aircraft carriers, and dozens of destroyers would attack and destroy the cream of the Japanese Navy.

Was It Worth It?

Hell no.

This is what the Japanese had left ready to fight on Dec 7, 1941.

• 3 light carriers
  • 2 Zuihō light carriers
  • Ryūjō
• 8 WWI vintage battleships (2 each of Kongō, Fusō, Ise, and Nagato)
• 16 Heavy Cruisers
• 19 Light Cruisers

And this is what the US Pacific Fleet had.

• 9 Battleships (some WWI)
• 3 Fleet Carriers
• 12 Heavy Cruisers
• 8 Light Cruisers

With the Canal knocked out it would slow, but not stop, the flood of ships from the Atlantic including 3 battleships, 2 fleet carriers, and any number of cruisers.

With the Japanese Navy taking on both the US and British navies, this would be sufficient to defend the Philippines leaving the US with a base deep in Japanese territory. The Pacific War would go down something more like expected in War Plan Orange.

Primary Sources

• University of Texas Libraries Perry-Castañeda Library Map Collection
• Guarding The United States and Its Outposts chapters XII and XIII.
• Biennial Reports of the Chief of Staff of the United States Army July 1, 1939 to June 30, 1941 to the Secretary of War
• Surface Distance Between Two Points of Latitude and Longitude
• Target Report - Japanese Bombs US Naval Technical Mission To Japan
• The Panama Canal by Frederic J. Haskin

Secondary Sources

• The Pacific War Online Encyclopedia
• Imperial Japanese Navy Page

Answer 2

The Canal is 8400 miles from Tokyo, compared to 4000 miles for Pearl Harbour. The Japanese carriers are stated of having a range of 10,000 miles at a cruising speed of about 16 knots, but remember that drag varies as the square of speed. Under battle conditions at speeds approaching 30 knots range would have shrunk to barely a quarter of that.

For a mission that far east of Pearl one must consider the entire sail back as being under battle conditions, potentially requiring not only a refuel upon approaching the target but 3, 4, or even 5 refuels on the way back, depending on how close to Pearl one dares venture. (Note that the great circle route from Panama to Tokyo goes right over Pearl.) Those tankers barely achieve 16 knots, so must be wandering around in the Eastern Pacific for a long time before and after the attack. To destroy this carrier force all that is necessary is to destroy one of the refueling flotillas.

Plus, the entire return mission probably needs to be performed under radio silence - note how a single poorly timed radio message ended the Bismarck's career earlier that year.

Couple the dangers of the mission with the difficulties of destroying, or even significantly damaging, the locks and gates of the canal, and the chances of the attack being successful are very low.

One note - it is probably better to sink vessels in the canal locks, turning them into sunken hulks, rather that the locks themselves. Several such sinkings would disable the locks for some time with a far better success rate than directly attacking the canal infrastructure.

This map of the North Pacific from Tokyo to Panama (red x's) shows a likely route from Japan to Panama that attempts to stay away from U.S. (and friendly)possessions. The busy sea and air routes from Vancouver and San Diego (and thus also San Francisco and Los Angeles) to Pearl are enclosed by the black lines. Note the distance, and thus time, spent east of Pearl.

Any attempt to approach Panama through the South Pacific is almost 3,000 miles longer, with consequent additional fuel requirements, plus the additional danger of being spotted wandering through Polynesia and Micro-/Mela-nesia while being hunted.

The actual attack on Pearl was launched while the Japanese carriers were somewhat west of the northernmost black line, about half way between its intersection with the blue line and Pearl.

Answer 3

Destroying those locks is going to be harder than you think. They are very large, at 110 feet x 1,050 feet, and the lock gates have to have been built to stand up to accidental collisions with large ships (at low speed, admittedly). They weigh up to 730 tons, depending on their height.

The best way to make the attack seems to be to use anti-ship torpedoes to attack the lock gates, dropping them into the locks, or the canal outside the locks. This needs to be done in a carefully organised way, because if one lane remains operational, the canal is still very useful.

Edit: The reason for using torpedoes is that they make it relatively easy to get an explosion in contact with the lock gate, which is hollow and can thus be flooded and made immovable until it is repaired and pumped out. Doing that with dive bombing is chancy: aviators always overstate their accuracy, and dive bombers could often miss ships entirely.

The correct gates to attack seem to be the downstream gates at the Pedro Miguel locks. Here, there is only a single lock in each lane, so there's less scope for aircraft attacking the wrong gate. You want to hit the downstream gates because there are two sets of upstream gates in each lane, as a precaution against floods.

If the downstream Pedro Miguel gates are destroyed, the canal remains usable, for smaller ships, because of the auxiliary gates half-way along each lock. Since those are normally retracted, attacking them is much more difficult.

The Japanese had the ability to refuel at sea, so they could have got some ships into position to make that attack. They probably could not have staged the entire Pearl Harbour task force out there, but nor would it have been necessary. The defences of the Pacific end of the canal don't seem to be all that strong. There is an infantry regiment, a coastal artillery regiment and an additional artillery battery. The Air Corps had a composite wing with 28 medium and 14 light bombers and 24 fighters.

The big risk of the mission is getting the attack force back afterwards. It will be thoroughly clear who has made the attack, and an intact US Pacific Fleet at Pearl Harbour is in an excellent position to cut off the Japanese force and destroy it.

I don't think the Japanese would have given the canal high enough priority to take that risk, given its limited practical effect and that they always concentrated on attacking military forces and neglected attacks on USN logistics throughout the war.

Edit: I also don't think they would have thrown away a pair of carriers (you need to send two so that an accident doesn't abort the whole mission) and their escorts and aircrew as the opening shot of a war. They didn't engage in suicide tactics until they were clearly loosing and the situation was desperate.

Answer 4

Canal locks may be much harder to destroy than you think. Ships can catch fire and they can sink. Canal locks won't do either.

As kind-of-evidence for this assertion, consider the St. Nazaire Raid. The Allies decided that they'd have to ram the gates of a dry dock with an explosives-filled destroyer. At the time, they had much heavier aviation at their disposal than the Japanese Navy.

You might also consider the Dambuster raids for a similar target.

Answer 5

Destroying the Panama Canal would have been extremely difficult and provide limited benefit. Many historians believe the Japanese wrongly targeted destroyers and battleships at Pearl Harbor, mostly due to the fact they thought they would play a more important role than submarines and aircraft carriers. They even neglected to disable the naval repair yards and oil reserves, which proved fatal, as the Pacfic Fleet was repaired in record time and faced no oil-supply shortages after the attack.

Attack on Pearl Harbor: Strategic Implications

Answer 6

The Japanese weren't "out" to destroy the Panama Canal. More to the point, they weren't even out to destroy Pearl Harbor (although they could have done so, in effect, with follow up attacks on the docks and fuel tanks).

What the Japanese wanted to do was to destroy or "cripple" the U.S.Pacific fleet, thereby setting back America's war effort by two years. And this fleet lay at Pearl Harbor, which is why Pearl was the target. By the time the U.S. fleet was rebuilt in mid to late 1943, Japan hoped to have completed its defense perimeter, including Midway, and the Fiji, Samoan, and New Caledonian Islands off Australia. They actually got about 90% of what they wanted.

They didn't count on American "persistence" (the main Pacific effort didn't begin until the fall of 1943, on the Japanese timetable). Nor did they expect America to get a "head start" by waging a war of attrition in the year before then.

As other posters have pointed out, the Panama Canal was twice the distance (or more) from Japan as Pearl Harbor. Destroying it without "catching" the American fleet would have been a highly risky affair for the Japanese fleet on the way back. Instead, Japan actually achieved most of its "stated" goal at minimum risk.

Answer 7

A successful attack on the Panama Canal was possible but under different circumstances and without the need Japans carriers.

Using a seaplane tender, with up to six Mavis flying boats could put the Panama Canal out of business for two-three years.

The Chitose, could leave from Kwajalein Atoll, Japanese territory. One ship, it would have to cross shipping lanes, but the trip would be half the distance than from Tokyo. At the same time, an oiler would leave, slightly different route but with a rendezvous schedule, to fuel up.

Any merchant ship seeing another ship, on the distance, is going to change course. The Chitose would do the same. Another merchant ship wouldn’t get close enough to identify it. This process was done to avoid German commerce raiders. They could go months without being seen, so it’s possible the Chitose could as well. If not, its actions would make it look like it was trying to stay away from another merchantman.

The Chitose sails to the Galápagos Islands. Even if seen, it’s a single ship, travelling the ocean. If identified, it’s peacetime.

The Mavi flying boats are painted like they are Panam flying boats (Mavis’s looking a lot like Panama flying boats) The Mavis flying in on differing routes to Panama, in early afternoon or otherwise same time as attack was heading in on Pearl. Three of the Mavis target the Gatineau Dam spillway gates. The other three target the Madden Dam. Two of them are loaded with high explosives. They land on the lake, right up against the dam, use scuttling charges to sink em next to dam, with timers. They sink, charges are set off taking out that dam. Water floods Gatun Lake, while the Gatun Dams spillways are damaged.

Some further info

• There were 3” aa guns at Gatun Locks, right next to the dam
• They were in revetments that prevented them from firing at too low a target. There was a shortage of crews, only 1 minute of ammo & crews weren’t well trained.
• The only radar working was the same as at Pearl & was at Pacific Ocean end. But, Pacific Ocean end was actually EAST of the Atlantic side. The mountains in southern Panama could obstruct the radar. Even if sited, they could be confused with Panam flights.
• Any patrol aircraft would probably be few, if any. First cuz it’s a Sunday, second cuz it’s early afternoon, not when an attack would be expected, third, it would be done by small individual aircraft not a massed swarm as would be expected, fourth, the aircraft would be under false colours and I’d seen wouldn’t likely be attacked
• At the time neither high command, or Pearl Harbour have issued an alert and no long range patrols have sited any issues
• At the time there were no torpedo nets protecting the dam spillways
• Bombs Or torpedos would only inconvenience the lock gates at best

In December, with losing all that water from BOTH dams would have put canal out of business for two to three years, per high commands estimates.

Alternatives?
Shipping rail traffic from east coast to west coast wasn’t much of an option. During wwii, USA expanded all ports on west coast considerably. As it was ships were waiting in port for three weeks before they got their turn to load up. Without the canal it would have been double that That leaves going around Douth America. In 1942, 1943, there was a severe shipping problem, merchantmen going around the Horn would have exposed merchantmen in the Atlantic to U Boats. That would have meant going in convoy which would have even worsen the shortage of shipping. Some merchantmen would have been lost going around the Horn. All operations in the Pacific would have suffered delays unless significant ships had been devoted which would have affected the war in Europe.

Answer 8

I think the Janpanese could have used a merchant ship in disguise loaded with tons of explosives. They would enter the canal and blow the whole thing just at the locks, destroy the locks and block the canal. Maybe they would use 2 or even 3 ships. This would simply avoid all logistic problems of a large navy raid and keep their naval battle force instact. No chance for the US navy to catch anything on the retreat...Just think St.Nazaire a little bigger.