Parameters for Kamikaze H6K's

[Shadow Master]

Ok folks, here is yet another crazy sounding idea brought to you by your local neighborhood Shadow Master.

In this thread, I'd like for a good discussion about using an H6K as a flying boat-bomb. The mission profile is to specially modify a number of these aircraft to put as large a payload as possible while retaining at least 2,000 range of their normal 4112 mile range. Fitting in extra fuel is of course fair game. Disassembling the aircraft to equip it with an internal yet 'drop-able' bomb is allowed/preferred.

What I am looking for here, is to have the modified H6K fly 2,000 some odd miles, land in a sheltered body of water, and while running across said body of water, deploy their payload while running at something less than takeoff speed.

********EDIT********
Like always, I goofed and failed to provide all the information needed. The discussion thread, where this idea was first posted, can be found here:
https://www.alternatehistory.com/forum/threads/h6k-as-a-flying-boat-bomb.430555/
I should have opened this 'how too' thread first if I had had a brain, instead of just jumping right in and discussing how to use them, as opposed to getting a consensus on what they needed to be able to do, in order for them to be useful. My bad.
********EDIT********

 

[Shadow Master]

So, it took me awhile to draw this, and then copy/paste parts over parts over parts, lol. But here is an extremely crude visual representation of the current state of the plan.

Ok, so I did warn that it was crude, right?
So, the Kamikaze H6K, specially modified to be able to deliver a massive bomb right into the under-the-waterline hull of an enemy warship, comes in as shown.

1) Upon reaching the battle area, the pilot selects his target, and lines up for their approach.
2) They then land, and continue to approach the target while in the water.
3) Once they reach "release point", they open the front and back of the modified hull, allowing the bomb to exit the back of the plane.
4) The bomb retains some forward momentum, and sinks deeper as it moves forward.
5) The bomb has 3 ways to detonate:

1. Contact detonation, either the ships hull/harbor bottom.
2. Depth gage detonation, upon reaching designed depth.
3. Timer detonation, to ensure detonation in case 1 & 2 do not work.

So, given this, and that this (Or something like it) is going to be developed and perfected by the IJN prior to the PH attack, any objections remaining to the possibility of a large explosive device, being accurately delivered by kamikaze aircraft, into the water right next to/underneath, the targeted anchored warship?

Any thought, or comments?

 

[Gannt the chartist]

Or you could use a torpedo bomber.

 

[misterwibble]

I'm sure the gunners on the ships would be delighted with such an easy target.

 

[Shadow Master]

I assumed that everyone reading this thread would already know about the other thread, but I guess I should have posted a link here.

Or you could use a torpedo bomber.

Yep, but then we wouldn't need a massive H6K, we wouldn't get the 4,000 lbs of explosives, and we wouldn't be able to make the OTL PH raid any more destructive than it was.

I'm sure the gunners on the ships would be delighted with such an easy target.

I'm sure they would, however, this is to be understood as an addition to the Dec 7th visit the IJN paid to PH, so, about those gunners...

 

[Archibald]

Why don't you use the H8K "Emily" ? it was a far better aircraft, armed to the teeth, good range, faster.

 

[Carl Schwamberger]

Best read the other thread. Most these questions addressed there.

 

[Shadow Master]

Why don't you use the H8K "Emily" ? it was a far better aircraft, armed to the teeth, good range, faster.

True, and the first came online in Jan, 1942.

Best read the other thread. Most these questions addressed there.

And as carl says, the other thread gives a much better picture of the proposed use of the H6K. I was looking at the improved engines, but the darn wiki doesn't tell me when they were ready.

 

[Shadow Master]

Here is a somewhat more complete version of the idea:

Hope this helps.

 

[trurle]

So, it took me awhile to draw this, and then copy/paste parts over parts over parts, lol. But here is an extremely crude visual representation of the current state of the plan.

Ok, so I did warn that it was crude, right?
So, the Kamikaze H6K, specially modified to be able to deliver a massive bomb right into the under-the-waterline hull of an enemy warship, comes in as shown.

1) Upon reaching the battle area, the pilot selects his target, and lines up for their approach.
2) They then land, and continue to approach the target while in the water.
3) Once they reach "release point", they open the front and back of the modified hull, allowing the bomb to exit the back of the plane.
4) The bomb retains some forward momentum, and sinks deeper as it moves forward.
5) The bomb has 3 ways to detonate:

1. Contact detonation, either the ships hull/harbor bottom.
2. Depth gage detonation, upon reaching designed depth.
3. Timer detonation, to ensure detonation in case 1 & 2 do not work.

So, given this, and that this (Or something like it) is going to be developed and perfected by the IJN prior to the PH attack, any objections remaining to the possibility of a large explosive device, being accurately delivered by kamikaze aircraft, into the water right next to/underneath, the targeted anchored warship?

Any thought, or comments?

Looks like insane hybrid of hydroplaning MTB and torpedo bomber. While definitely technically possible, Japanese IOTL would have problems building such a device until ~1944. They simply had no mathematician in position to properly design hydroplaning hulls. H6K and H8K hulls were designed by "trial and error" method, not having a proper model. Later photos of American MTBs helped a bit though.

Likely design may work to some degree, but utility would be limited, because the craft would be very vulnerable on final run and strike distance would be virtually point-blank - much more vulnerable compared to torpedo bomber or even torpedo boat. Also, the attack would be more dependent on weather compared to normal torpedo attack.

P.S. IOTL, the ship-killing attack has developed in opposite direction since carronades - relatively smaller charges thrown from larger distances, and i believe were good reasons (partly improvements in fire control, for both ship defense and ship killing) for evolution of warfare going this way but not an opposite.
Branders went extinct. Bomb ships too. Torpedo ships are nearly extinct. The next cruising missiles are facing increasing challenges.

 

[Shadow Master]

Thanks you sir.

Looks like insane hybrid of hydroplaning MTB and torpedo bomber. While definitely technically possible, Japanese IOTL would have problems building such a device until ~1944. They simply had no mathematician in position to properly design hydroplaning hulls. H6K and H8K hulls were designed by "trial and error" method, not having a proper model. Later photos of American MTBs helped a bit though.

As the H6K is a working seaplane, in 1938, we don't really need anything else beyond that, so we can proceed with the pinpoint accuracy achievable under good (Historical PH raid) conditions.

Likely design may work to some degree, but utility would be limited, because the craft would be very vulnerable on final run and strike distance would be virtually point-blank - much more vulnerable compared to torpedo bomber or even torpedo boat. Also, the attack would be more dependent on weather compared to normal torpedo attack.

I think that we are well past the "work to some degree" point by now, surely. As far as utility, well yes, this is something of a niche role, as landing is going to be restricted to sheltered waters. Attacks against underway ships pose a big problem, even if the ships are in sheltered waters, and if they are in the open seas, then an alternative attack profile would have to be used. Any use of these H6K in a tactical combat environment, without total air superiority and surprise, is going to be quite costly, even without adding in AA and AAA fire from the target and/or escorts. In fact, just about the only use for this type of an attack, is the one being posited, a surprise attack, against enemy ships at anchor, with the expectation of friendly fighters keeping any defending fighters busy long enough for the attack to be made.

As BlondieBC pointed out in the other thread, I was probably being conservative when I posited a 4,000 lbs charge. Without skimping on fuel, we would likely be easily looking at northwards of 5,000 lbs of high explosives, but let us split the difference and call it 4,500 lbs of high explosives, or ten times that of an OTL Type 91 of the kind historically used in the PH raid.

Any thoughts on the effectiveness of these monster charges upon tightly packed small craft?

 

[trurle]

As the H6K is a working seaplane, in 1938, we don't really need anything else beyond that, so we can proceed with the pinpoint accuracy achievable under good (Historical PH raid) conditions.

I meant the possibility the semi-ditched H6K will go out of control in the instant the bomb bay opened or bombs jettisoned. You basically need to develop smooth transition between 3 hydro/aero-dynamic states: normal hull (tested in 1938), hull with open bay and bomb (untested), and hull with open bay without bomb (untested). From development perspective, version with explosive high enough to do not touch water during gliding may be more practical. In case of high-mounted bombs, even if loss of control happens, bombs are already separated by about meter from any part of aircraft.

I think that we are well past the "work to some degree" point by now, surely. As far as utility, well yes, this is something of a niche role, as landing is going to be restricted to sheltered waters. Attacks against underway ships pose a big problem, even if the ships are in sheltered waters, and if they are in the open seas, then an alternative attack profile would have to be used. Any use of these H6K in a tactical combat environment, without total air superiority and surprise, is going to be quite costly, even without adding in AA and AAA fire from the target and/or escorts. In fact, just about the only use for this type of an attack, is the one being posited, a surprise attack, against enemy ships at anchor, with the expectation of friendly fighters keeping any defending fighters busy long enough for the attack to be made.

As BlondieBC pointed out in the other thread, I was probably being conservative when I posited a 4,000 lbs charge. Without skimping on fuel, we would likely be easily looking at northwards of 5,000 lbs of high explosives, but let us split the difference and call it 4,500 lbs of high explosives, or ten times that of an OTL Type 91 of the kind historically used in the PH raid.

Any thoughts on the effectiveness of these monster charges upon tightly packed small craft?

Yes, approximately the set of roles you outlined. Actually limited scope is very similar to Kaiten submarines - who had very severe opposition during development in IJN. The opposition would be even more severe for H6K flying bomb (skimming bomb may be more proper name?) due to higher cost of the H6K airframes.

Regarding efficiency of 4500 lb (2000 kg) skimming charge, it would be definitely deadly for destroyers, light cruisers, auxiliary carriers, converted civillian vessels and such. Newer and heavier vessels starting from may be Independence class carriers (11 kt) are more than 50% likely to survive a single direct hit, although are very likely to be disabled.

 

[Pangur]

So, it took me awhile to draw this, and then copy/paste parts over parts over parts, lol. But here is an extremely crude visual representation of the current state of the plan.

Ok, so I did warn that it was crude, right?
So, the Kamikaze H6K, specially modified to be able to deliver a massive bomb right into the under-the-waterline hull of an enemy warship, comes in as shown.

1) Upon reaching the battle area, the pilot selects his target, and lines up for their approach.
2) They then land, and continue to approach the target while in the water.
3) Once they reach "release point", they open the front and back of the modified hull, allowing the bomb to exit the back of the plane.
4) The bomb retains some forward momentum, and sinks deeper as it moves forward.
5) The bomb has 3 ways to detonate:

1. Contact detonation, either the ships hull/harbor bottom.
2. Depth gage detonation, upon reaching designed depth.
3. Timer detonation, to ensure detonation in case 1 & 2 do not work.

So, given this, and that this (Or something like it) is going to be developed and perfected by the IJN prior to the PH attack, any objections remaining to the possibility of a large explosive device, being accurately delivered by kamikaze aircraft, into the water right next to/underneath, the targeted anchored warship?

Any thought, or comments?

How does this work? The aircraft has landed so how does it get to drop a bomb? Secondly, even the most jaded sailor would spot the aircraft coming their way note that its not an allied aircraft and react

 

[Shadow Master]

How does this work? The aircraft has landed so how does it get to drop a bomb? Secondly, even the most jaded sailor would spot the aircraft coming their way note that its not an allied aircraft and react

True, the aircraft are not going to land undetected. Possibly the aircraft is recognized as not being an American design. "Drop" may be leading you to some wrong visualizations, let us say instead 'jettison' or simply 'release', to get folks to see that there isn't going to be a period of free fall through the air for this payload. The goal is to get the warhead to detonate well below the surface, like a torpedo, and crush the targets torpedo defense system, and sink the ship.

This use of an H6K as a Kamikaze aircraft is going to be limited to making the first strike at pearl harbor much more telling than the OTL strike could have been. Without additional carriers, we really cannot make the KB do all that much more damage than OTL if we still want to hit the airfields hard in the first wave. So how to augment the first waves attack, but without having additional carriers in the battle? The H6K have a 4,000 mile range, and can hit pearl harbor on a one way trip all the way from the marshall islands. A B5N2, can deliver a type 91 torpedo, over a much shorter distance, but these carry 450 lbs of explosives. The H6K's are carrying 4,500 lbs of the same explosives (so, ten times as much), and are meant to one-shot the USN battleships. So, no carrier aircraft can carry such a weapon, nor operate at such a distance from it's base, and throwing 25 of these Kamikaze aircraft into the mix gives the IJN a vastly more potent hitting power.

Looked at purely from the weight of underwater explosives being able to be delivered, the 25 H6K are bringing the equivalent of 250 torpedoes to the battle. Historically, the 4 USN battleships in battleship row at the start of the attack took 15 torpedoes, which sank 3, and the 4th beached itself to avoid sinking. In this posited attack, the H6K are going to be dealing with all the heaviest ships, as their weapons are much more capable of killing a battleship than a type 91. It should be noted, the type 91's had no trouble sinking USN battleships they hit, with even just 2 hits, so these H6K are NOT going to fail to do the job with far more powerful weapons! This then frees up the carrier planes to seek out more, weaker ships, and sink a great many of them. OTL, the IJN wasted 12 torpedoes on the USS Oklahoma(5) and USS West Virginia(7), but in this alternate attack, all those torpedoes can be sent against pacific fleets CA's, CL's and DD's.

The other part is, as in OTL, the small numbers of US sailors stuck on board, on duty, on a sunday morning, are not on a war footing, so about the time they realise they are actually under attack, is about the time the first Kamikaze slams into the side of one of the battleships, with it's bomb detonating shortly thereafter. Within a very short time thereafter, say five minutes or less, all the remaining H6K have made their attacks, and now it is the turn of the KB first wave.

 

[Shadow Master]

So, any questions or thoughts about the feasibility of the rather novel concept of using some large, long range flying boats to deliver far more powerful underwater detonating explosive charges, from a great distance away, as an additional part of an ATL pearl harbor raid?