Militärbas i USA tränar på att skjuta ner Kims robotar

North Korea has conducted a total of five nuclear tests, in 2006, 2009, 2013 and twice in 2016, 2017.

The explosive yield of a nuclear weapon is the amount of energy released when that particular nuclear weapon is detonated, usually expressed as a TNT equivalent (the standardized equivalent mass of trinitrotoluene which, if detonated, would produce the same energy discharge), either in kilotons (kt—thousands of tons of TNT), in megatons (Mt—millions of tons of TNT), or sometimes in terajoules (TJ). An explosive yield of one terajoule is 0.239 kt of TNT. Because the accuracy of any measurement of the energy released by TNT has always been problematic, the conventional definition is that one kiloton of TNT is held simply to be equivalent to 1012 calories. The yield-to-weight ratio is the amount of weapon yield compared to the mass of the weapon. The practical maximum yield-to-weight ratio for fusion weapons (thermonuclear weapons) has been estimated to six megatons of TNT per metric ton of bomb mass (25 TJ/kg). Yields of 5.2 megatons/ton and higher have been reported for large weapons constructed for single-warhead use in the early 1960s. Since then, the smaller warheads needed to achieve the increased net damage efficiency (bomb damage/bomb weight) of multiple warhead systems, has resulted in decreases in the yield/weight ratio for single modern warheads.

Kärnvapen är en typ av vapen vars sprängladdning får sin energi från fission, eller från olika kombinationer av fission och fusion, av atomkärnor, till skillnad mot konventionella vapen, vars sprängladdningar får sin energi från kemiska processer. Kärnvapen finns i varianter från de minsta med sprängkraft som inte är mycket större än de största konventionella bomberna, till enormt kraftfulla konstruktioner som kan utplåna allt inom en radie på flera kilometer. Kärnvapen transporteras vanligen till målet med bombplan eller ballistiska robotar, men även artilleripjäser, kryssningsrobotar och minor med kärnladdningar finns. Många kärnvapen har provsprängts men endast två har använts i en väpnad konflikt: Atombomberna över Hiroshima och Nagasaki (Little Boy och Fat Man) sprängdes mot slutet av andra världskriget i augusti 1945 på order av USA:s president Harry S. Truman. Den som använder kärnvapen i en väpnad konflikt bedriver kärnvapenkrig.

Fort Greely is a United States Army launch site for anti-ballistic missiles located about 100 miles (160 km) southeast of Fairbanks, Alaska. It is also the home of the Cold Regions Test Center (CRTC), as Fort Greely is one of the coldest areas in Alaska, and can accommodate cold, extreme-cold, and temperate-weather tests depending on the season. It is named in honor of Major General Adolphus Greely. There was an earlier Fort Greely on Kodiak Island.