North American B-70 Valkyrie. It was a very large, very high altitude, and very fast, bomber that was developed into two prototypes that flew a lot of test flights.
This aircraft, not the SR-71, is what prompted the soviets to develop the Mig-25 interceptor.
With a nuclear payload, great range, the ability to cruise at 1988mph, and sprint faster, and come in higher than any anti aircraft missile system in use at the time could reach, it scared the Soviets something awful, especially since they knew we could do it.
One was lost in a terrible accident when an F-104 chase plane drifted too close and was drawn into striking the tail of the bomber. The second prototype continued to fly for a while before being grounded when the program was canceled. It survives today on display at the Wright Patterson museum.
The Arado E.555
Designed by the German Arado company during World War 2, the E.555 was meant to be a German long range strategic bomber with jet engines.
It could carry a total of 4 000 kilograms worth of bomb load and a range of 7 500 kilometres.
The range of the E.555 would’ve been even longer than America’s iconic B-32 Dominator who had a range of 6 118 kilometres. Its payload will dwarf the British Wellington who carried 2 000 kilograms worth of explosives.
Furthermore its top speed of 875 – 920 kilometres per hour was much faster than the best US fighter at the time, P-51 Mustang which flew at 703 kilometres per hour.
Ultimately, the E.555 bomber was cancelled by 1944, when the Germans were running low on resources and funds.
The Boeing–Sikorsky RAH-66 Comanche is the most advanced attack helicopter ever conceived. The design program cost SEVEN BILLION DOLLARS (FWIW, a Nimitz aircraft carrier costs $4.5 billion). We built two prototypes and then cancelled the entire program, because attack helicopters had already been rendered obsolete by drones. The US military will never buy another attack helicopter ever again.
Here are both Comanche prototypes – your seven billion tax-dollars at work:
