Monaghan spent the next few years serving in the Atlantic fleet but was transferred to the Pacific fleet in time to take part in the attack on Pearl Harbor. She was serving as the ready-duty destroyer and was just about to steam to the aid of USS Ward (DD-139) at the entrance of the channel when the attack began. Soon after, Monaghan received notice that a submarine had been sighted; it proved to be a Ko-hyoteki class submarine and Monaghan subsequently rammed and depth charged the midget which then sank.
Monaghan also served in the Battle of the Coral Sea, Battle of Midway, and the battle of Komandorski Islands (March 1943). After almost three years of war, Monaghan was lost in a typhoon in November of 1944, with only six of her crew surviving.