Battle_of_the_River_Plate The Battle of the River Plate (December 13, 1939) was the first major naval battle in World War II. The German pocket battleship (heavy cruiser) Admiral Graf Spee had been commerce raiding since the start of the war in September. It was found and engaged off the estuary of the River Plate off the coast of Argentina and Uruguay in South America by one of the hunting groups set up by the British Admiralty to search for the Graf Spee, comprising three smaller Royal Navy (RN) cruisersHMS Exeter, HMS Ajax and HMS Achilles, which was part of the RN's New Zealand Division.