North Korea’s development of an operational ballistic missile submarine would pose additional challenges for the U.S. as it works to defend itself and its allies from the rogue nation’s burgeoning missile program. As war on the Korean peninsula becomes increasingly possible, the U.S. and its allies are working to prepare themselves in case North Korea launches a ballistic missile at them. Throughout 2017, North Korea continued to test missiles that experts believe are capable of reaching major cities in the U.S. like New York and Washington D.C.