I can't claim to know that my submission is the single most expensive military machine. Likely it would be dwarfed by the Manhattan Project, and maybe beaten by a few more projects as well. But per unit, I think my choice will at least have a place on the list.

Now, in recent years, a billion dollar project isn't that rare. Even a billion dollars for a single plane is not unheard of. But the Valkyrie bomber project cost 1.5 billion dollars--in 1950's and 60's money--and delivered two aircraft. Two. And then one got ran into by a friendly aircraft during a photo opportunity, and it was "the good one."

I first ran into the Valkyrie as a child. The museum now known as the National Museum of the U.S. Air Force is located in Dayton, Ohio. This put it on the route between my home and a set of relatives, and my dad indulged my budding love of history by stopping off. I was amazed by the biplanes, and entranced by the WWII warbirds. The jet fighters were pretty neat, too. But then we ended up in the big hangar. I went from plane to plane, making my way around the displays. I eventually ran out of hangar to explore, and was next to a wall. I looked up. I was staring into six of the biggest engines i had ever seen. I scampered around to find more information.

As it turns out, I was looking at the only surviving example of a heck of a plane. It was designed to fly at Mach 3 at over 70,000 feet to strike targets in the Soviet Union. The fact that it could achieve those feats starting in 1964 was astonishing. But, those same figures were its downfall. Designed as a high-altitude penetrator, it was supposed to fly higher than anything that could bring it down. However, developments in anti-aircraft missiles meant that the Valkyrie was quite within range from the ground. And when you tried to go in low--like the B-52 was able to do--the tradeoffs necessary to achieve those lofty figures quoted above were just too drastic. The Valkyrie was barely faster than a B-52 on the deck, and its fuel economy left a good deal to be desired. Also, the bomb bay was limited in relation to the Stratofortress. The Valkyrie was an engineering marvel, but it was made obsolete before it was even built by the engineering marvel of the anti-aircraft missile.

There was just enough momentum in the program to get two examples built. The first one had some problems in its construction, as there were some new processes being used. The second example righted many of these problems. Then there was a request for a photoshoot. Sadly, one of the pilots flying an F-104 fighter in formation with the larger bomber got too close, and the wings of the two planes made contact. The F-104 pilot and one of the two pilots of the Valkyrie were killed. That happened in 1966, and the plane was retired in 1969. That is when it was flown to Dayton, there to wait until it astonished a young kid with six huge engines.

Now, again, I can't promise that 750 million dollars per unit in 1950's and 1960's dollars is the most expensive military machine. In fact, it probably doesn't. But I can say I have kicked the tires (gently, and only as a kid, I got a bit smarter and more respectful as I aged) on a one of a kind masterpiece of engineering that cost a mint.

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If you have an hour, and don't mind cheesy military videos, this link should give you a ton of info

Also, the Valkyrie is no longer readily available to be viewed at the museum. It is still free, but you have to sign up to take a bus trip to the R&D hangar. The museum is well worth the trip, and the side trip to the R&D hangar and the presidential aircraft hangar are worth the time as well.