Why did Commodore Harwood concentrate his force off the River Plate?
Graf Spee sank her first victim, the Clemant on September 30th. There followed five other victims before the Doric Star on 2nd December 1939 and the Tairoa the following day. Both ships transmitted raider reports which alerted Harwood to the probability that Graf Spee was heading towards South America. However Graf Spee’s ninth and final victim, Streonshalh did not manage to transmit a raider report when she was attacked.
Harwood decided that Langsdorff had three likely options if he was approaching South America. He would reach waters off Rio de Janiero (Brazil) by 12th December, off the River Plate (Argentina and Uruguay) by the 13th December or be at the Falkland Islands by 14th December (the anniversary of the destruction of Admiral von Spee’s squadron in 1914 during World War 1 fell on 8th December). Of these, the most threatening to British trade, and therefore the most likely, was the River Plate with its valuable grain and meat trade carried on British merchant ships.
On 3rd December Harwood ordered Ajax, Achilles and Exeter to meet on 12th December at a rendezvous 200 miles east of the River Plate estuary. Cumberland was to continue with planned maintenance at the Falkland Islands. In order to confuse allied intelligence, Graf Spee had been operating under the name Admiral Scheer (her sister ship), which was actually undergoing a refit in Germany at the time. It was not until after the battle when she was in the River Plate estuary that Graf Spee used her own radio call sign and the British forces knew the true identity of their opponent.
Graf Spee in the Atlantic