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The X-61A Gremlins is a unmanned air vehicle, which is being developed by the Dynetics Gremlins team for the Defense Advanced Research Projects Agency (DARPA) Gremlins programme.
X-61A Gremlins Air Vehicle (Infographics)
550km range at Mach 0.6?
Hahaha haha aaand ha. :)
Jetstream tailwinds are totally legit considerations .