Since summer, 2012, rebels have seized control of large swathes of land near the Turkish and Iraqi borders to the north and east, respectively, and used these areas to organize their forces and build supply lines.

NPR: Head Of Western-Backed Syria Rebel Coalition Quits

Thus, the U.S. has sought to organize its nuclear forces so that no enemy can launch a disarming first strike, mainly by fielding three distinctly different types of weapons: manned bombers, land-based intercontinental ballistic missiles in hardened silos, and sea-based intercontinental ballistic missiles on stealthy Trident submarines.

FORBES: Nuclear Weapons: How Few Is Too Few?