What were the relative strengths of the two forces?
Graf Spee was of 12,000 tons displacement. Her main armament was six 11 inch (280mm)guns in two triple turrets firing shells weighing 670 lbs (303kg) to a maximum range of 40,000 yards (36.5km) but with a rate of fire of only two to three rounds per gun per minute. She could not divide the fire of her main armament in order to engage separate targets. Her secondary armament of eight single 5.9 inch (150mm) guns, four on each side, fired 100 lb (45kg) shells to a maximum range of 24,000 yards (22km). She also carried 4.1 inch (100mm) AA guns and eight 21 inch (533mm) torpedo tubes. Her armoured belt was of 3 inch (76mm) thickness which was believed to have been capable of keeping out shells of 8 inch (200mm) calibre and below. Her turrets were protected by 5.5 inches (140mm) of armour. She was powered by long range MAN diesel engines giving her a designed speed of 28 knots (52kp/h) though she never achieved more than 24 (44kp/h) during the battle.
HMS Exeter was of 8,400 tons displacement and carried six 8 inch (200mm) guns in twin turrets which fired 250 lb (113kg) shells to a maximum range of 30,000 yards (27.5km) with a rate of fire of about 6 rounds per minute. Her armoured belt was of similar thickness to Graf Spee’s but her turrets were only lightly armoured. She carried three 21 inch (533mm) torpedoes each side and two Walrus amphibious aircraft designed for reconnaissance and spotting gunfire.
HMS Ajax and HMS Achilles were each armed with eight 6 six inch (150mm) guns in four twin turrets firing shells of 100 lbs (45kg). Their maximum gun range was slightly less than Exeter’s with a rate of fire of 8 to 9 rounds per minute. They carried four 21 inch (533mm) torpedoes each side. Ajax carried a single Seafox float plane but Achilles was not carrying one.
The steam-powered turbines of all three cruisers gave them a maximum speed of about 30 knots (55kp/h) but it took time to work up to this.
Graf Spee had overwhelming fire power which could cripple a cruiser with one or two direct hits from her main armament in the right place, but her rate of fire was slow. The British ships had the important advantage of speed but only Exeter’s shells were able to penetrate Graf Spee’s armour.
During the battle much depended on the skill and tactics of the two opposing commanders.
Admiral Graf Spee