When I was 12, I wanted to be an astronaut. Several things screwed this up. The first one being that I suffer from major motion-sickness. I have to dope myself up to the gills to not heave up my latest meal should I travel by boat or plane or train. (Another thing being that I'd have to join the air force and do well in it, but that's another story.) I do okay in cars for some reason.
The big reason for motion sickness has to do with your vestibular system in your ear. When what you see doesn't match what your system reports the local gravity to be, your body concludes that you're in a whirlpool, and decides that you need to be a little lighter to escape. Up comes your stomach contents. The misery of this also attempts to condition you to not jump in whirlpools, fool. One big problem of this is that it's not a whirlpool, it's a plane, and you can't exactly just jump out of it anytime you feel like.
Then some time ago, I saw a TV program in which physicist Michio Kaku is given something out of science fiction, and told to try and describe a way to have it really happen, as best physics will allow. This particular episode was about "destroying the death star," the pivitol scene from the movie "Star Wars." His version was very different from the movie. One of the things he had to work with was G-Force, in which inertia plus a fast turn proves really, really bad for pilots. Each "G-Force" is an increase in force above what is felt due to gravity, so a pilot experiencing five g-forces is thrown with 5 times the force of earthly gravity. Air force pilots routinely suffer 7 g-forces, and astronauts experience ten. Both require elaborate systems to stay conscious by reducing the effect this has on them. Too many g-forces can prevent your brain from receiving blood, causing you to pass out, and too much more can smash your body to pulp. Dr. Kaku's solution was to immerse the pilot in water. Buoyant force counteracts the inertial force, so even as the water experiences 7, 10, or 50 g-forces, it also distributes it so that your own body doesn't feel them. He proved this with a water balloon in a centrifuge. The balloon in an air filled beaker was flattened by the force. The balloon floating in water retained its shape, no matter how fast the centrifuge went.
This makes me wonder if I flew in a tank of water, if maybe I wouldn't get motion sick. The plane could experience all the turbulence in the world and I wouldn't feel it. I'd need some sort of breathing system, as we humans don't have gills or skin-breathing the way animals that live in water do. If everyone was in tanks like that, you could not bother pressurizing the cabin, just a breathing tube in the tanks. Flying would be a more comfortable, if soggier, experience. I say this because there is a limit to cabin pressurization. The more the plane is pressurized, the harder the forces on the hull, and more than about 8.6 psi is an intolerable risk. Too much pressure and the plane simply pops like a balloon. A balloon made of metal. Not fun for anyone, but even worse for those inside it. So even with pressurization, flying in a plane is like a trip to Tibet. You have much less oxygen, and it's woozy and difficult and your sense of taste is diminished from the low pressure. In tanks, you could get a sea-level amount of air and breathe normally.
The air force would also be interested in this technology. A pilot that flew in a water-filled cockpit could turn harder and faster than one in a conventional cockpit, as he would be without the risk of blacking out. This probably makes it worth the extra weight. Especially if competing planes don't have such a system. Enemy nations would face planes that could abruptly turn around and destroy them from positions that were previously thought of as totally vulnerable. Dives could be further and faster with fewer consequences. Mobility in general would vastly improve.