Shipbucket

Would it be theoretically possible to design a submarine capable of launching aircraft?
If so, has it been done before?
I assume the submarine would have to be of significant size to house even a single small fighter-bomber, but how big would one need to be to house a squadron of fighters? (By squadron, I mean roughly 12 aircraft.)
What sort of aircraft today would be ideal for doing so? (If there is one.)
I'm guessing that you could launch an aircraft off a submarine with a catapult using the same basic principles as with an aircraft carrier, but I'm no expert on the subject.
Assuming that you did have a submarine large enough to house a squadron of aircraft, and you could use a catapult to launch said aircraft, how would you land the aircraft back on the submarine after a mission?

(I put this in General Discussion since the concept may play into the AU I'm working on.)

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- Miles

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Balkans AU Concept - Postponed for now, maybe
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Yes it has been done in the past, mostly interwar vessels. The British M submarines, the French Surcouf and the various Japanese large subs come to mind for ones that experimented with aircraft. The Germans trialled it in WW1 and then in WW2 experimented with autogyros and early helicopters however in all cases it was largely impractical. It took far too long to assemble, launch and recover an aircraft whilst all the while the submarine had to remain vulnerable on the surface.

Also for a submarine to be able to carry an aircraft, it has to be big or have a bulky hangar structure on deck. This causes the sub to be very noisy underwater, making it easy to detect. The boat would also be sluggish underwater and the hangar is a great big void space just waiting for a depth charge to rupture it and flood it, making the sub unstable in trim.

That is why all the Navies except for the IJN abandoned the idea before WW2 began and I can't think of any real occasions in the Pacific War that the Japanese actually used their aircraft carrying submarines with the aircraft other than the il-fated plan to bomb the locks of the Panama Canal.

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"The first rule is not to lose; The second rule is not to forget the first rule"

Hmm... Would there be any way to muffle the noise underwater?
I'm thinking that that would be the main drawback, rather than the sluggishness and the large hangar area.
I'd also say that the submarine would only surface briefly to launch its aircraft, then submerge again until the aircraft came in to land.
The main purpose of the submarine would likely be to get close to enemy coastlines before launching aircraft on missions against port cities, but the aircraft could also be used for antisubmarine warfare, if equipped with torpedoes. If there was a way to muffle the sound of the submarine, I'm thinking that speed would not be as big of an issue. Also, if a submarine is larger, does this give it the capability to dive deeper? If so, then wouldn't the submarine be able to go deeper than smaller, lighter subs would to navigate past them?

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- Miles

My Shipbucket List (See what I did there?)

Balkans AU Concept - Postponed for now, maybe
Some other AU thing

Hold on... you said that the main problem of the submarine was that it had to stay above water while the aircraft were assembled, launched, and recovered. What if the submarine didn't have to do that for the recovery? What if the aircraft had a small amount of underwater maneuverability to enable them to dive before "docking" (for lack of a better word) with the submarine, allowing the submarine to stay underwater for the recovery process? I'm assuming this is completely unfeasible, but it's just a thought.

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- Miles

My Shipbucket List (See what I did there?)

Balkans AU Concept - Postponed for now, maybe
Some other AU thing

Actually smaller submarines are able to dive deeper as the pressure hull can be close to the ideal spherical shape for handling the pressure. As for muffling the sound, technology can help but it is limited as regardless you're going to have lots of issues with hydrodynamic noise over the hull.

As for the aircraft themselves, you're going to need something that can land on the ocean. This means not only floats but also that the design can handle the sea swell and highly corrosive environment. Also on that note, you would only be able to launch aircraft in a very rare smooth calm sea as a submarine is not a good platform for operating aircraft. Your best bet would be to float the plane off into the sea and have it take off and land under its own power.
This is of course ignoring the fact that such a niche mission is really not worth developing an entire new form of warfare for and the fact that the drawbacks with both the submarine and aircraft design you would have to have defeat any potential benefits.

If you want to operate aircraft, get an aircraft carrier or use long range land-based aircraft with or without air to air refuelling. The idea of a submerging aircraft carrier that so often appears in sci if and fantasy is completely flawed and impractical.

As for submerging aircraft, that is an awful idea from the get go. An aircraft is fragile, designed to handle the air. Water is highly destructive and combining both roles would present endless engineering issues and even if possible would result in a machine that can barely do either role. We can hardly produce cars that can drive on water, trying to make something that could fly and dive would be all but impossible and even if you could do it, there would be no purpose.

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"The first rule is not to lose; The second rule is not to forget the first rule"

I see. An interesting concept, but hardly a practical one. You mentioned that a spherical shape is the perfect shape for a submerged object. Does the size of said submerged object matter?

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- Miles

My Shipbucket List (See what I did there?)

Balkans AU Concept - Postponed for now, maybe
Some other AU thing

Well its a matter of material strength in relation to the cross-section, as we know a toy metal car can handle more scaled punishment than a real car as the steel is, while thin, has the same tensile strength, Ideally you want to find the largest size possible that doesn't impact on the integrity of the pressure hull greatly, a fifty foot diameter hull will last less under pressure than a 25 foot hull.

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I've seen this worked out before, so this post will derive heavily from others work - work that was done for a 32 fighter craft not a 12 fighter craft (which dramatically worse because on 12 airframes you can generate a CAP or a strike, but not both). Cost on that hull was estimated to be about 30 Billion USD (or 5 CVNs, or 30 AVNs) with a top speed of 14 knots submerged, 10 knots surfaced.
Very large. The least-bad way of doing this would be to raft together a series of pressure hulls about the diameter of those used on the Ohio class boats. I'd go for not less than four hulls wide and one two hulls underneath (likely the lower row would be either two or three hulls wide). You are also looking at a sub substantively longer than an Ohio.
Either STOVL aircraft (Harrier, JSF) or a seaplane (Convair Sea Dart).
Problematic to do. Better to avoid the catapult all together.
Either land on water beside the craft or vertically on the craft.
Spheres are the strongest shapes, but for storing equipment that we want to remove a cylinder is better.
Size of submerged cylinders is limited by the quality of the steel used. While we can use something like HY-130 on the hull (rather than HY-100 used on the Seawolf and HY-80 used on the Ohio), we're going to limit the dive depth to no greater than 400 feet - so we can close the ends of the tubes to get the planes in and out. This means that a 50'-70' hulls are possible.

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The main question is why would you want to do that? What mission or capability would the aircraft provide that is not better provided by organic submarine capabilities?

If you wanted a recoverable strike platform, the carrier can provide that better. If you wanted some kind of ISR capability you'd have to keep your submarine at or near the surface to recieve the information and then you would run into mast height problems. Your submarine would be limited to about 12 nautical miles from the launched aircraft.

One idea might be to have a torpedo launched drone that would break the surface and then begin a preprogrammed ISR mission. The drone could be recovered by a surface asset at a set time, so the surface group could use all the intel collected.

There's a reason submersible aircraft carriers never became a Thing outside of a few token/experimental uses...

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