So, where exactly would these air-deployed mini-subs be used?
Near an enemy harbor won’t work, because the planes would be spotted.
Near your own coastline wouldn’t be necessary, because you have plenty of time to deploy from ships.
In the open ocean is kinda pointless, because that what full-size subs are for.
I can only see two use cases for this. One would be for quickly deployed shore defense, as if you’ve just captured an island or just discovered the site of an enemy assault. (In which cases secrecy is less of an issue; you may even want to deter the enemy so they turn back.) The other would be something like the Battle of Midway, where you might be able to predict an enemy fleet’s position well enough to get subs in position, but still far enough away that you’re not seen doing it.
Don’t DROP them, you might break them. Sling them between the pontoons of float planes. The float plane skids to a stop in the water, and the sling lowers the minisub into the water, and the plane surges forward into the air again.
That’d be one big-ass float plane to lift that much weight.
My first thought was a flying boat. I don’t know that you’d be able to deploy the sub straight down, though; you’d need a hull strong enough for a water landing that could open like a bomb bay. You might be able to open the afterbody (the part of the hull after the step), but you probably don’t want the weight shift when you’re unloading to take the whole tail under water.
Maybe a double-hull flying boat, like joining two PBYs together at the wing root with the sub slung between the fuselages would work.
Except there is no way to specifically target a keel or propeller; particularly with unguided torpedos, you aim for where trigonometry says amidships will be (hopefully in full profile aspect) and loose the fish.
The reason this was never done is because it isn’t a good plan.
Not really. “Float plane” usually refers to those with external pontoons, like this. A plane like the Spruce Goose, where the bottom of the fuselage forms the water-borne hull (like this), is called a “flying boat”.
I wouldn’t quite agree with that, and the Wikpedia entry for seaplane says that it differs between British and American usage.
My initial response was that “seaplane” refers only to small aircraft, some of which are flying boats with a buoyant, stepped fuselage/hull. That’s probably just a personal bias, though. Large flying boats were well on the way out before I was born.
So a “seaplane” is any plane that can take off and land on water.
Nitpick: the H-4 Hercules ‘Spruce Goose’, didn’t actually fly until 1947, and then only one flight of less than a minute that never rose above the ground effect regime.
The largest fixed wing aircraft ever flown in an operational capacity is the Antonov AN-225, with a payload of 250 tonnes (internal)/200 tonnes (external). This would be large enough for something the size of a small “full-sized” WWII submarine/u-boat, but again, the boat wouldn’t survive the drop onto the ocean’s surface.
