U.S. Marine Sgt. Daniel Castro instructs a Marine in

U.S. Marine Sgt. Daniel Castro instructs a Marine in throwing a M67 hand grenade during the exercise Fuji Viper 20-1 in Camp Fuji, Japan, Oct. 23, 2019. Fuji Viper is a regularly scheduled training evolution for infantry units assigned to 3rd Marine Division as part of the unit deployment program. The training allows units to maintain their lethality and proficiency in infantry and combined arms tactics. Castro is assigned to 4th Marine Regiment, 3rd Marine Division, and a native of Cayey, Puerto Rico. (U.S. Marine Corps photo by Lance Cpl. Michael Estillomo)