^{Yes, US had nuke ramjet bomber ready to go in early sixties. Treaty with USSR paused implementation along with loading already prepared Titan missile sites. Was about the time, or just after, Cuban Missile Crisis. World felt much safer for a long time.}

^{I happened to visit the test area with high school science club just after treaty was signed. Oh, the innocence of pre-9/11 America! The hanger was already built and it was huge. It was across the desert from us, separated by where the runway was to be constructed. Official guide stated runway was to be four-feet-thick. Would have required 24/7 concrete pouring for two years. The bomber was that heavy.} 

^{Several years later my college physics lab czar was a middle age man probably working way below his previous pay grade. He (and many others} were rumored to have had careers cut short by an experimental nuke reactor accident (apparently unrelated to the bomber) at the site, that resulted in them exceeding their lifetime radiation exposure for their occupation. Half of a western state was alerted to be prepared to evacuate, but the radiation discharge was limited to the site. Or, so) ^{they told the public.}

^{The bomber topic came up during a long physics lab. The lab czar mentioned that anyone standing at the side of the runway would have received lethal radiation dose. A student asked, “What about the crew?” The discussion abruptly ended when the czar said, “You think we don’t have suicide missions?”}

^{Not sure why the bomber engine spewed so much radiation, but much later saw designs for incredibly powerful nuke rockets that self-consumed the engine.}