Members of the 320th Missile Squadron missile combat crew work through a scenario in the 90th Operations Support Squadron's Missile Procedure Trainer on F.E. Warren Air Force Base, Wyo., in June 2014. The MPT is a simulator that allows missile crews to practice contingencies they might face while on alert.
R.J. Oriez/U.S. Air Force
President Obama, speaking in Prague in 2009, said: "I state clearly and with conviction America's commitment to seek the peace and security of a world without nuclear weapons." While Obama has pushed for a reduction in nuclear arms throughout his presidency, he has also agreed to an expensive upgrade of America's aging nuclear arsenal.
A North Korean man reads a local newspaper on Sunday with an image of leader Kim Jong Un. Kim said during a critical ruling party congress that his country will not use its nuclear weapons first unless its sovereignty is invaded, state media reported.
Kim Kwan Hyon/AP
People watch a news report at a railway station in Seoul on Feb. 3. North Korea launched a long-range rocket Sunday local time, defying international criticism.
Jung Yeon-Je/AFP/Getty Images
Sumiteru Taniguchi, 86, a survivor of the 1945 atomic bombing of Nagasaki, walks up to deliver his speech at the 70th anniversary of the atomic bombing in Nagasaki, southern Japan, on Sunday.
A Minuteman III missile engine is loaded into a truck for transport to another building for X-raying before being torn down and rebuilt. The Air Force's missile command-and-control structure has been the subject of several recent scandals.
Douglas C. Pizac/AP