The Army is developing a new hand grenade, capable of either fragmentation or concussive effects. A team at the Army’s Armament Research, Development and Engineering Center at Picatinny, N.J., is working on the device, which would allow users change from fragmentation to concussion by flipping a switch. Once the device enters the inventory sometime around 2020, it will mark the first time soldiers had access to concussion grenades since their use was discontinued in 1975 because of concerns about asbestos.