Air Force Magazine
In the 1950s and early 1960s, the Air Force pushed to be the space force for America. As part of that drive, the service proposed building a reusable spaceplane, the X-20 DynaSoar.
The X-20 was conceived as an operational system to conduct space missions of reconnaissance, satellite inspection and repair, orbital resupply, and bombardment.
The third version was to use a Titan IIIC rocket booster and have an orbital capability. This variant would contain a bomb bay for delivering nuclear warheads requiring precise targeting and would offer the ability to approach a target from any direction.
Eventually deciding against placing nuclear weapons in space, the Defense Department canceled the first test version of the X-20—less than a year before testing was to have begun in 1964.
US officials preferred smaller, more accurate warheads, unlike their Soviet counterparts, who had a “bigger is better” philosophy. For US leaders, the prospect of a gigantic nuclear weapon coming down accidentally was highly worrisome.
That, plus America’s ability to rely on a large, highly versatile fleet of manned bombers, kept the United States from seriously pursuing an orbital nuclear weapon.
http://www.airforcemag.com/MagazineArchive/Pages/2005/June%202005/0605FOBs.aspx
