HMS Cumberland narrows Graf Spee's breakout window

At about 10:00 on 14 December, the County-class heavy cruiser HMS Cumberland had joined HMS Ajax and HMNZS Achilles off the River Plate. In this assessment, her arrival marked the point when Graf Spee's practical chance of escape closed, well before Ark Royal and Renown arrived. HMS Exeter, Ajax, and Achilles had already inflicted enough damage to force the German ship into port, and the waiting cruisers remained prepared to finish the fight at severe cost. Any movement by Graf Spee would be reported at once, giving the blockading ships time to go to action stations. Cumberland's eight-inch guns, backed by the two light cruisers that had already fought Graf Spee, made the harbor exit a much more dangerous tactical problem.