Hrmm, the relatively high pressure of water could simulate the relatively high effective pressure of very high velocities in air. So... rocket-boosted submarines? Trained to fight in various unusual formations with tactics designed to take advantage of one of the members jumping to, say, 120kph for a couple of minutes, and likely drowning out all the other sonar contacts in the area, in order to set up an ambush or get the bait out of trouble quickly, or even to rush into the enemy ranks and remain too close to the enemy capital ships to be easily engaged... And the knowledge gained from getting a submarine to work under such influences could translate to a jump-start on the supersonic aircraft chassis... Although, admittedly, without proper tactics to support it, it would be a massively useless gimmick...
P.S.
Does anyone have ideas for how to intercept the UFOs? Especially AA guns & tactics besides filling the sky with bullet, and hoping one hits. If we go for fighters, well, "How to put a gun onto a glorified Bell X-1."
The only other option I can see is full-on orbital invasion. Of spaaace!
Why a Bell X-1?
HE 176: 1939, estimated 750 kph. Only a prototype.
Me 163: 1941, recorded at 1130 kph in 1944. Terrible performance in the war, against massed formations of much slower, much longer-ranged opponents who could wait for the fuel to run out and only needed to worry about a couple of passes. Against a single opponent who can't be bother to hunt down a single opponent and is moving at ludicrous speeds? The dynamic changes completely, a single pass is likely all that you will get regardless, engagement times for any one craft are miniscule, and running out of fuel and using a parachute to get to the ground, possibly with the craft itself abandoned because there are very few engagements so we can afford to be wasteful... The problems pretty much all vanish and it starts to become an issue of how we can throw away all the established benefits of the design and amplify everything that caused problems... Rapid response is important, but we can afford air patrols and if it doesn't need to take off or land then we can ignore some aerodynamic issues...
Ohka: Broke a destroyer in two. Useful in itself at destroying highly resilient and well-defended surface targets(like landed aliens) but was generally a failure because of fighter interception against the motherships outside of its 37km range. The aliens have a 15 km range... Unfortunately, SOME of our designers lack the courage to do what must be done...
BI-1: Kind of terrible, but had a throttle... I suggest that we focus on solid-fuel drop-tanks until we have something that can engage the enemy in the air, then try to transition to other technologies...
I mean, sure, the X-1 was fast, but it was ahead of our time and didn't do what we want. The Me 163 was a proven design that is largely contemporary and is a victim of design constraints that do not apply to our situation. We do not need rapid response, we can just keep a couple-dozen in the air at all times, carried by bombers, and release them if an enemy happens to enter into range. We can afford to lose the craft so a small craft-based parachute to stabilise for the pilot to bail would be sufficient and the agility is not required, so all things considered we can go for an even shorter flight-time and a less buoyant chassis... We do not need to match the enemy performance, just get fast enough to intercept their position and maintain a decent firing window and I like to think that we could get the speed difference well under 1000kph. Ideally we would have a couple of dozen craft each attacking from a couple of different directions...
I am tempted to spend a design phase just building a wind tunnel. We could get our technology up in the process of building an impractically large device capable of propelling air at, say 3000 kph? And then using it gives us a bonus to our chassis design...