Benefiting from their First World War experience, the British started convoys as soon as war began. It paid off: between September 1939 and the following May, 229 ships were sunk by U-boats but only twelve of these were sailing in convoy. The organization of the convoys was managed, despite the difficulties of making the civilian ships’ captains do things the Royal Navy way, and there were fast and slow convoys to accommodate ships of varying performance. The layman usually supposes that it was the protection given by escort vessels that made it safer to go in convoy, but this was not so. Churchill provided the true reason:
The size of the sea is so vast that the difference between the size of a convoy and the size of a single ship shrinks in comparison almost to insignificance. There was in fact very nearly as good a chance of a convoy of forty ships in close order slipping unperceived between the patrolling U-boats as there was for a single ship; and each time this happened, forty ships escaped instead of one.6
The basic Dönitz tactic was to have surfaced submarines patrol across known shipping routes until one of the lookouts spotted a convoy. The radio monitoring service in Germany, with its ability to read the secret British merchant ship code, helped Dönitz to position his ‘rake’ of boats. The first submarine to sight a convoy sent high-frequency radio signals to a master control room ashore, and made medium-frequency signals to nearby submarines to bring them to the convoy.
At night on the surface the U-boats engaged the merchant ships independently, and often at point-blank range. Before daylight came, they ran ahead to concentrate for another attack on the following night, the submarine’s surface speed being faster than its speed underwater.
The Admiral Graf Spee action
Submarines were not the only threat to Britain’s sea lanes. Admiral Graf Spee and Deutschland had put to sea a few days before war began. Construction of these cruisers had been started before Hitler came to power, when the peace treaty restricted Germany to ships of less than 10,000 tons. Perhaps in reaction to the way in which the Royal Navy had lost three cruisers at Jutland by single well placed shots, these Panzerschiffe (‘armour ships’) were given thick armour and big guns. Newspaper writers called them ‘pocket battleships’ but they were designed to prey upon merchant shipping. Their innovations included electrically welded hulls. Welding requires metal to be heated to an even temperature; for that reason the welding of thick steels is vastly more difficult than welding light aircraft alloys. The new ships had very shallow draught, and their honeycombed hulls reduced the danger from torpedoes. Heavy top-side armour protected them from air attack and their 11-inch guns had a range of 20 miles. They were powered by diesel engines – which until that time had only been used as auxiliary engines in such vessels – and could steam at 26 knots, an unimpressive speed for a cruiser but suitable for a raider. Each warship had a tanker at its disposal.
The Deutschland was assigned to raid the routes of the North Atlantic. She sank two merchant ships and captured a third (the City of Flint sailing under a US flag) and then returned to Germany, skilfully using the long November nights to elude the Royal Navy blockade. Her two-month voyage had destroyed 7,000 tons of small shipping; it was a disappointing debut for the ‘pocket battleship’. Soon she was renamed Lützow because Hitler feared the propaganda effect of a mishap to a ship named Deutschland.
Admiral Graf Spee was sent to the sea lanes of the South Atlantic and the Indian Ocean. By 7 December 1939, in a voyage that included the South African coast and South America, she had sunk nine merchant ships. The captain, Hans Langsdorff, a handsome fifty-year-old, had strict ideas about the rules of war. His targets were sunk without loss of life, his prisoners were all treated well and German morale was high. His only setback was a cracked engine block in the battleship’s spotter plane and no spare to replace it.
When Graf Spee sank the Trevanion in the South Atlantic on 2 October 1939, the men in the Admiralty had looked at their charts and guessed that the raider would head for the shipping lanes of South America. They stationed HMS Ajax off the River Plate, the New Zealand warship Achilles off Rio de Janeiro, and HMS Exeter off Port Stanley in the Falklands. But the next signal was an RRR – ‘raider sighted’ – from the tanker Africa Shell off the East African coast. Had Graf Spee’s captain immediately sent a signal to inform Berlin of his success things might have ended quite differently for him; there would have been no way of guessing whether he was bound for the Indian Ocean or back into the South Atlantic. But Langsdorff waited ten hours, and when his signal was transmitted, three British Direction Finding Stations took a bearing on the signal. These bearings were sent to London on priority channels but even the Hydrographic Section at the Admiralty had no charts large enough to plot them.
Fortunately Merlin Minshall, a young officer of the Volunteer Reserve, had bought a globe four feet in diameter. It was, he calculated, ‘equivalent to a flat chart nearly twelve feet from top to bottom … Within seconds I had placed three thin loops of rubber round my newly acquired globe. Their intersection clearly showed that the Graf Spee was heading not north up into the Indian Ocean but south back into the Atlantic.’7 It was 4 o’clock in the morning. Rear Admiral ‘Tom Thumb’ Phillips, the vice-chief of naval staff, arrived dressed in a scruffy kimono to see the globe which was too big to be moved. ‘Good idea using the globe,’ he said. (Admiral Dönitz had come to the same idea as Lieutenant Minshall and was using a similar globe in his situation room.)
More sinkings confirmed this route. Graf See was in the southern hemisphere and 13 December 1939 was an idyllic calm summer’s day. Visibility was perfect and at 0614 hours Graf Spee’s spotters saw the heavy cruiser HMS Exeter (8-inch guns) and turned towards her. The Graf Spee had six 11-inch guns and Langsdorff assumed that the two vessels with Exeter were destroyers escorting a merchant shipping convoy of the sort that Graf Spee was seeking as prey, but without the use of his spotting aircraft he was unable to confirm this.
In fact Langsdorff was heading towards one of the many ‘hunting groups’ that were looking for him. Exeter had seen Graf Spee’s smoke and had turned towards it. And the destroyers Langsdorff had spotted were actually light cruisers: HMS Ajax and the New Zealand navy’s Achilles (each with eight 6-inch guns). He was probably misled by the fact that both ships were of unusual profile, having single funnels serving boilers sited together so as to economize on weight.
These three ships provide three different answers to the question that had plagued the world’s navies for half a century: what should a cruiser be? Should it be a light vessel, fast at 32 knots with small 6-inch guns like the Ajax and Achilles; should it be of medium weight like the Exeter, with 8-inch guns; or should it be a heavy ship with massive 11-inch guns that make it so formidable that it is called a pocket-battleship but unable to exceed 26 knots? No wonder the camouflage experts had painted a huge white wave curling from the Graf Spee’s bow. It would never make such a wave in real life – and now