In November and December 2017, China’s People’s Liberation Army (PLA) Air Force conducted at least nine long-distance training flights over maritime areas along China’s periphery, continuing a trend that began in 2015. Since 2015, long-distance over-water training has become more frequent, featured a greater variety of aircraft, and extended into areas in which the air force had not previously operated. The long-distance over-water training is part of a broader PLA Air Force effort to transition from a service focused on territorial air defense to one capable of conducting offensive and defensive operations beyond China’s coast. These flight activities potentially challenge U.S. interests by (1) improving the PLA Air Force’s capability to execute maritime missions against the United States and U.S. allies and partners in the region; (2) gathering intelligence against the U.S. military and U.S. allies and partners; and (3) reinforcing claims in maritime disputes and pressuring Taiwan.