H6K as a Flying Boat-Bomb.

[Insider]

The H6K could take 2 torpedoes, or 2 800kg bombs, which were the 406mm AP shells in fact. It could also lift 2 tons of explosive instead. I feel something like that could be pulled of, actually, but...
1. The targets should be softer than battleships - a cruiser or aircraft carrier would be just perfect. As it turned out rightfully so, because these ships did the most of the job, while BB's rusted moored in harbours. I don't know if Japanese were able to alter their thinking enough to alter the targets, as their doctrine called for weakening US battleline first.
2. things as dry docks, or fuel tanks should be next in line, one plane one target rule should be taught to pilots
3. The strike should come low long before approaching PH, to minimalise chance of being detected by radar. I don't know how much Japs knew enough about US radars, to make it a concious decision.
4. The airplanes should be painted to resemble Catalina flying boat. I know there were many differences, but these wouldn't be distinguished until it is too late. What is more likely, that the approaching flying boat is a Catalina or an enemy?
5. If the attack come out of the blue, there was quite a chance for success. The ships would have doors in watertight compartments opened, and while I understand that this is war, the base feel safer than the seas around. If identified, each flying barn covers over 5 km a minute. The question is how fast you can get to the gun, and get it working.
6. Regardless the damage, the biggest damage would likely come from fear of another such attack, simply by forbidding US troops R&R and soaking up AA guns and crews.

However the aspect that doesn't suit me here is the Kamikaze attack in the first months of war. I understand the heavy damaged airplanes were sometimes diverted by their pilots to hit the enemy, however, such happy forgoing pilots' lives doesn't feel IJN on the eve of war. Only later when the situation got desperate the Kamikaze attacks become a reality.

 

[Wimble Toot]

Did you miss the part about this being done on dec 7th, 1941, as a part of the initial air attack?

No, but I caught the bit about it being a monumentally stupid idea, so stupid the even the Imperial Japanese Navy, a organisation not renowned for its tactical sanity, didn't even consider doing it.

If they painted it olive drab and put US markings on it, it might stand a chance.

But I doubt it.

Something that can barely carry a short ton of bombs isn't going to have much impact.

 

[iddt3]

Kamikazes were a desperation move by a loosing power that no longer had quality pilots. It's like asking what if Germany used the Volkstrum for the invasion of Russia - they wouldn't. The IJA and IJN we're insane, yes, but that doesn't mean they were going to start what they thought would be a short victorious war with tactics that went against every piece of doctrine they had, as well as wasting their fantastic prewar stable of pilots.

 

[Wimble Toot]

There was a kamikaze attack on Pearl Harbor on 07/12/1941.

There are two main reasons why this is a stupid idea.

1) Flying boat arrives early for attack: removes element of surprise for the effective main assault.

2) It arrives during or after the attack, USAAF aeroplanes and USN will shoot it down, before it even gets close to anything.

 

[eltf177]

There was a kamikaze attack on Pearl Harbor on 07/12/1941.

There are two main reasons why this is a stupid idea.

1) Flying boat arrives early for attack: removes element of surprise for the effective main assault.

2) It arrives during or after the attack, USAAF aeroplanes and USN will shoot it down, before it even gets close to anything.

#1 was why Yamamoto was against the midget subs, which did exactly this (they got lucky the report wasn't believed until too late)...

 

[marathag]

I don't know - 5,000 pounds of explosive is an awful lot. I see a LOT of topside damage taking some time to fix. And on a more lightly built ship like a carrier with fuel and explosives it could be much worse.

USS Cole, estimated 4-700 pounds of plastic explosive delivered by small boat

 

[Wimble Toot]

USS Cole, estimated 4-700 pounds of plastic explosive delivered by small boat

WW2 ships were marginally better armoured than that missile-equipped spam can.

 

[Zheng He]

#1 was why Yamamoto was against the midget subs, which did exactly this (they got lucky the report wasn't believed until too late)...

 

[Richard V]

Not only were harbors heavily defended, but capitol ships come and go, it be difficult to predict what targets are in port. Perhaps such an attack could be mounted on a fixed target like the Panama Canal.

 

[Zheng He]

What about trying something wacky like crashing remote controlled explosive laden H6Ks into a target? Like the mission Joe Kennedy Jr was killed on.

 

[marathag]

WW2 ships were marginally better armoured than that missile-equipped spam can.

All or Nothing, for the most part. USS Nevada. lots of area protected by thin STS steel

and if you get a little below the waterline before exploding

this is 180 pounds of guncotton in a mine did

 

[marathag]

What about trying something wacky like crashing remote controlled explosive laden H6Ks into a target? Like the mission Joe Kennedy Jr was killed on.

Heroic aviators far easier to find

 

[trurle]

So, in a thread where the Japanese somehow have 1 or more atomic bombs on Dec 7th, 1941 to hit PH with, it came up that the H8K, that was about to enter service in January, 1942, would have the range to carry a 10,000 lb atomic bomb from the home islands to PH, on a one way trip.

This thread has nothing to do with Japanese Atomic bombs! But the wheels started turning because of that other thread, and so...

Let suppose that the Japanese have made contingency plans for an invasion of Hawaii, either as the opening moves in a war against the USA, or as something for later on. Let us further suppose that as preparations for such plans, the Japanese explore the possibility of using some of their existing H6K's as basically flying bombs, loaded with all the high explosives that they can carry, and all the fuel to give them the range to hit PH either from their bases in the Marshall islands, or possibly with a refueling stop in French Frigate Shoals, as the historical 1942 raid on PH did.

What kind of tonnage of high explosives could such a Kamikaze flying boat/bomb pack in, and what kind of damage would result of an attack successfully impacting an anchored battleship have? What other high value targets could warrant such an expenditure, other than other capital ships?

Several post were made to note what the flying bombs are less effective than torpedoes in sinking the capital ships. This is essentially true. The quality can be substituted for quantity though.
The question basically boils to the "how much explosive H6K can carry with realistic modifications of late 1941?".

I can imagine the following scenario:
1) Strip the fleet of 16 H6Ks of defensive equipment, crew seats beside one, torpedo mounts, rear armour, redundant bulkheads, bomb bay doors
2) Make them ditch at Japanese fleet location few hundred km from Pearl Harbor, ventilate most of fuel tanks and pour the already-melted TNT from pre-assembled machine into fuel tanks. Do not wait for solidification.
3) Board one kamikaze pilot to each of H6Ks.
4) Spice the contraption with contact detonators liberally

Such arrangement would turn each of H6Ks into short-range flying bomb. With roughly 10-12 tons TNT equivalent.

The next question is how to attack. Best available option may be shallow dive profile - because it maximizes the speed and reduce the exposure to the short-range AA fire. Heavy AA fire could be assumed to be absent in the case of surprise attack. I roughly estimate 2/3 of aircraft will hit their targets, most striking amidships far from waterline. The H6K, especially when shallow-diving at ~380 km/h, would be difficult to down by the light automatic AA fire before striking the target, therefore most failures would be failure to aim the overloaded and possibly damaged aircraft.

The last question is how much damage would be done to battleship-sized target if struck by essentially 20-ton mortar charge with 10-ton filling. Scaling from torpedo hits and reducing destructive power by factor of 4 (the ships upper structures are typically has average density 1/4 of water, and the most of structural damage is done by accelerated water/debris, not by exploding gases itself). Largest (0.5 ton warhead) torpedo were known to punch roughly 10-meter holes in warships.
The H6K flying bomb in most powerful configuration would wreck a total destruction in diameter ~10*sqrt((10/0.5)*0.25)=22 meters. On typical 30-kt battleship this mean heavy damage (likely mangling superstructure, killing by over-pressure majority the crew exposed on decks and destroying one of the turrets), but not sinking the battleship outright. The damage is likely to be fatal for any vessel up to the largest of the light cruisers though (up to the 10-kt Brooklyn class), simply breaking them in halves.

Therefore, my conclusion: to sink an average US battleship of 1941, each would need approximately 3 strikes of H6Ks in ultimate "flying bomb" modification. Not practical because repeated strikes would have a lower chance of passing through, and risking overkill by ordering simultaneous strikes on the same battleship would be very discouraging for the kamikaze pilots. Many would pull out from damaged target to have the opportunity to make a more decisive strike instead of coup de grace. Cruisers would be much more vulnerable though - so may be it would be wise to target US cruisers and auxilliaries (which were largely spared IOTL Pearl Harbor attack) with flying bombs while reserving torpedo bombers for the battleships.

Actually ordering to kamikaze pilots is the nearly impossible task. IOTL on final run, they tended to ignore all the mission briefings and simply attacked the largest available target into its geometric center or slightly higher- to minimize the risk of total failure. Imagine the feelings of such a pilot. The limited time, perspective of certain death, and control difficulties of plane in previously unflown configuration, with the airframe not intended for such sort of attack at all. Pilot would naturally feel the extreme stress, with biggest fear to miss the target at all.

I expect what even if all 16 pilots would be ordered to attack cruisers, only half of them will comply, with the rest attacking battleships anyway.
Forecast is 4 cruisers sunk, 2 cruisers heavily damaged, 1 battleship sunk, and 4 battleships damaged in the attack by 16 H6K flying bombs.

 

[Wimble Toot]

How many battleships did the Mistel, with the hollow charge warhead actually sink?

More than one? (which was already sunk anyway)

 

[Shadow Master]

Such arrangement would turn each of H6Ks into short-range flying bomb. With roughly 10-12 tons TNT equivalent.

Ye gods, man! This is an interesting counter proposal, but the mission you are proposing is far harder to pull off than my more conservative version. Thanks though for the input.

The next question is how to attack. Best available option may be shallow dive profile - because it maximizes the speed and reduce the exposure to the short-range AA fire. Heavy AA fire could be assumed to be absent in the case of surprise attack. I roughly estimate 2/3 of aircraft will hit their targets, most striking amidships far from waterline.

For your version, that may be the best, however, my version doesn't need to "dive from above, and end up exploding on the upper decks", but rather to crash into the sides of the anchored ships.

Do me a favor, and if you can, and give us the differential equations between a 450 lb warhead detonation at {insert the depth the OTL raid had their torpedoes set to}, vs the detonation of some 4,000 lb of the same explosive just at or below, the waterline. The reason I persist in stipulating a water detonation is that I remain unconvinced that the Japanese would be unable to work out a way to make that happen. I frankly doubt that there is really any valid engineering limitation that would proscribe such from being within their capabilities. So, if you have the math and physics {That I lack}, throw me a bone and provide the requested info.

So basically, 450 lbs detonating at normal depth, or 4,000 lbs detonating {at the waterline --- as a worst case}. Which one does more damage?

 

[Grand Admiral Thrawn]

Ye gods, man! This is an interesting counter proposal, but the mission you are proposing is far harder to pull off than my more conservative version. Thanks though for the input.
For your version, that may be the best, however, my version doesn't need to "dive from above, and end up exploding on the upper decks", but rather to crash into the sides of the anchored ships.

Do me a favor, and if you can, and give us the differential equations between a 450 lb warhead detonation at {insert the depth the OTL raid had their torpedoes set to}, vs the detonation of some 4,000 lb of the same explosive just at or below, the waterline. The reason I persist in stipulating a water detonation is that I remain unconvinced that the Japanese would be unable to work out a way to make that happen. I frankly doubt that there is really any valid engineering limitation that would proscribe such from being within their capabilities. So, if you have the math and physics {That I lack}, throw me a bone and provide the requested info.

So basically, 450 lbs detonating at normal depth, or 4,000 lbs detonating {at the waterline --- as a worst case}. Which one does more damage?

Why did you cut out the part where @trurle pointed out

"Actually ordering to kamikaze pilots is the nearly impossible task. IOTL on final run, they tended to ignore all the mission briefings and simply attacked the largest available target into its geometric center or slightly higher- to minimize the risk of total failure. Imagine the feelings of such a pilot. The limited time, perspective of certain death, and control difficulties of plane in previously unflown configuration, with the airframe not intended for such sort of attack at all. Pilot would naturally feel the extreme stress, with biggest fear to miss the target at all."

That is a key problem you face, and it not an engineering problem, but a human problem, which, since technology is not advanced enough, your idea relies on. How are you going to change OTL? Give them a more comprehensive training than the carrier pilots got? Rather expensive throwing away great pilots, your plan relies on average pilots.

 

[trurle]

Ye gods, man! This is an interesting counter proposal, but the mission you are proposing is far harder to pull off than my more conservative version. Thanks though for the input.
For your version, that may be the best, however, my version doesn't need to "dive from above, and end up exploding on the upper decks", but rather to crash into the sides of the anchored ships.

Do me a favor, and if you can, and give us the differential equations between a 450 lb warhead detonation at {insert the depth the OTL raid had their torpedoes set to}, vs the detonation of some 4,000 lb of the same explosive just at or below, the waterline. The reason I persist in stipulating a water detonation is that I remain unconvinced that the Japanese would be unable to work out a way to make that happen. I frankly doubt that there is really any valid engineering limitation that would proscribe such from being within their capabilities. So, if you have the math and physics {That I lack}, throw me a bone and provide the requested info.

So basically, 450 lbs detonating at normal depth, or 4,000 lbs detonating {at the waterline --- as a worst case}. Which one does more damage?

4,000 lbs above waterline will do approximately twice the structural damage of 450 lbs under waterline. I do not count flooding damage here though.

Regarding horizontal attack profile, it may be not practical due kamikaze pilot limitations. H6K was not an easy aircraft to fly even in normal circumstances. Add absence of 2nd pilot (increasing forces on control stick), overload and aerodynamics change due added explosives, the lower approach speed and need to freuently apply control inputs at low altitude - and you will get the recipe for the extreme pilot fatigue and high risk of just crashing in water (not really acceptable by kamikaze pilots) in low-altitude approach. Also, the need to pull down in the last second to strike target (cannot realistically make approach below decks level) will make nearly all kamikaze pilots extremely nervous. Even if ordered, many if not majority of kamikaze pilots will break low-altitude approach, go up a bit, point nose to the center of target, trim control surfaces for the zero forces on stick, and will watch the target gradually gets larger in the forward sight.

 

[Shadow Master]

Why did you cut out the part where @trurle pointed out

"Actually ordering to kamikaze pilots is the nearly impossible task. IOTL on final run, they tended to ignore all the mission briefings and simply attacked the largest available target into its geometric center or slightly higher- to minimize the risk of total failure. Imagine the feelings of such a pilot. The limited time, perspective of certain death, and control difficulties of plane in previously unflown configuration, with the airframe not intended for such sort of attack at all. Pilot would naturally feel the extreme stress, with biggest fear to miss the target at all."

That is a key problem you face, and it not an engineering problem, but a human problem, which, since technology is not advanced enough, your idea relies on. How are you going to change OTL? Give them a more comprehensive training than the carrier pilots got? Rather expensive throwing away great pilots, your plan relies on average pilots.

I like your approach, that you described in another thread as like onto taking a hammer to an idea, and see what is left over, so something like that.

I cut out quite a bit more than just that part, to be honest, because I want a comparison made between a water-level detonation of some 4,000 some odd lbs of explosives vs 450 lbs detonated at historical depth.

Now, as for the rest;
Some of the bolded portions...

1) Actually ordering to kamikaze pilots is the nearly impossible task.
2) IOTL on final run, they tended to ignore all the mission briefings and simply attacked the largest available target into its geometric center or slightly higher- to minimize the risk of total failure. Imagine the feelings of such a pilot.
3) The limited time, perspective of certain death, and control difficulties of plane in previously unflown configuration, with the airframe not intended for such sort of attack at all. Pilot would naturally feel the extreme stress, with biggest fear to miss the target at all."

1) I wouldn't be ordering anyone to undertake such a mission, I'd be offering a chance to die in glorious battle for those who volunteer and pass the rigorous selection process, and make it through the very tough training program.

2) Listing problems from OTL late war Kamikaze attacks, where the situation is not at all what is being posited in this thread, at least, not by me, contributes little, as this mission is going to be well prepared for, well trained for, and well-rehearsed, unlike later war missions.

3) Turtle went and totally rewrote the aircraft for the raid, that, among other things, requires the aircraft to undergo modifications in the field, in the enemies' back yard as it were, as an integral part of the plan, and with the pilots now flying aircraft that don't handle like before. My plan doesn't do that.


Now for your part...

That is a key problem you face, and it is not an engineering problem, but a human problem, which, since technology is not advanced enough, your idea relies on.

This is, of course, not going to be anything at all like the problem it is being made out to be. The Japanese population had been fed a line of hogwash about how noble and glorious it was to give selfless service to the Emperor, including sacrificing one's life in the process, and all that jazz, for how many years? So getting some young and idealistic hotshot pilots to volunteer for such a mission is not going to be a deal breaker. Read up on the choices made by IJA troops when faced with surrender or death in the island battles throughout the whole of the war. Self sacrifice was ingrained by the Japanese school system for years before WWII.

How are you going to change OTL?

I don't need to change OTL with respect to getting folks on board with this mission type.

Give them a more comprehensive training than the carrier pilots got?

Let's say simply, nearly as good as the carrier pilots, as they don't actually have to land on a carrier deck...

Rather expensive throwing away great pilots, your plan relies on average pilots.

Can you quote me, from anywhere in this thread, where I said anything about using other than Japan's Best? Hint, look at posts #5 and posts #13.

 

[Shadow Master]

4,000 lbs above waterline will do approximately twice the structural damage of 450 lbs under waterline. I do not count flooding damage here though.

Can I though, finally get what I asked for, and know what a below the water detonation is going to do? I'm not an engineer, but I have no doubts whatsoever that the clever Japanese are going to know that an underwater detonation is preferable to an above water detonation, and that they are going to easily be capable of devising a means to achieve this, and most likely, without any difficulty.

Thanks for your time and input!

 

[Grand Admiral Thrawn]

The OTL problem, @Shadow Master is that if they are not the best, they have the problems @trurle mentioned of panicking at the last minutes and deciding to hit the center of the ship, and not at the waterline. I don't mean OTL as in finding them, you only want 16 or so, right? There were thousands. But how will your 16 avoid the OTL problems of panicking? We have OTL evidence of kamikaze pilots (of average to less than great quality) doing it. If you train them better than carrier good, then you are throwing away great pilots. But great pilots might be the only ones able to achieve the hits you want. Psychology hasn't improved enough by 1941 to figure out which ones are good pilots but great under pressure, so able to fly into the waterline.

And I think trurle meant ordering the pilots to aim for the waterline, not in finding them