Police officers shot a "flash-bang" grenade into an Ocean Beach apartment late Thursday, then burst through the doors and arrested three men on narcotics charges. A San Diego police spokesman said the grenade, which makes a loud noise and a brilliant flash of light, was used as a diversionary tactic because the resident was known to answer the door with a gun in hand. Robert Walker King, 28, was booked on suspicion of possession and sale of narcotics. Berhard Dale Howard, 48, and Bennett Joseph Bratton, 22, were arrested for suspicion of possession of narcotics. Amphetamines and substances that were believed to be hashish and cocaine were seized in the raid, which culminated a three-month investigation by the Narcotics Task Force. A shotgun was found by the door, the spokesman said.