The number of U.S. Marines killed in aviation accidents this year has reached 18, the highest in five years, according to NBC News. The previous record was set in 2012 at 15 accidents. Five separate incidents are responsible for the death toll. Notably, three of the five occurred during rotorcraft training missions. On May 10, a UH-60 Black Hawk crashed off the Florida coast in heavy fog, killing seven. On May 17, an MV-22 Osprey crashed in Hawaii, killing two. On Sept. 2, a CH-53E Super Stallion crashed during an advanced rope exercise near Camp Lejuene, North Carolina, killing one.