Editing Battle of the Atlantic (section)

==Early skirmishes (September 1939 – May 1940)==
{{For timeline|Timeline of the Battle of the Atlantic}}
In 1939, the {{lang|de|Kriegsmarine}} lacked the strength to challenge the combined British Royal Navy and [[French Navy]] ({{lang|fr|Marine Nationale}}) for command of the sea. Instead, German naval strategy relied on commerce raiding using [[capital ship]]s, [[armed merchant cruiser]]s, submarines and aircraft. Many German warships were already at sea when war was declared in September 1939, including most of the available U-boats and the "pocket battleships" {{ship|German cruiser|Deutschland||2}} and {{ship|German cruiser|Admiral Graf Spee||2}} which had sortied into the Atlantic in August. These ships immediately attacked British and French shipping. {{GS|U-30|1936|2}} sank the [[ocean liner]] {{SS|Athenia|1922|6}} within hours of the declaration of war—in breach of her orders not to sink passenger ships. The U-boat fleet, which was to dominate so much of the Battle of the Atlantic, was small at the beginning of the war; many of the 57&nbsp;available U-boats were the small and short-range [[Type&nbsp;II U-boat|Type IIs]], useful primarily for [[Naval mine|minelaying]] and operations in British coastal waters. Much of the early German anti-shipping activity involved minelaying by [[destroyer]]s, aircraft and U-boats off British ports.

With the outbreak of war, the British and French immediately began a [[Blockade of Germany (1939 - 1945)|blockade of Germany]], although this had little immediate effect on German industry. The Royal Navy quickly introduced a convoy system for the protection of trade that gradually extended out from the British Isles, eventually reaching as far as [[Panama]], [[Bombay]] and [[Singapore]]. Convoys allowed the Royal Navy to concentrate its escorts near the one place the U-boats were guaranteed to be found, the convoys. Each convoy consisted of between 30 and 70 mostly unarmed merchant ships.

Some British naval officials, particularly the First Lord of the Admiralty, [[Winston Churchill]], sought a more 'offensive' strategy. The Royal Navy formed anti-submarine hunting groups based on [[aircraft carrier]]s to patrol the shipping lanes in the [[Western Approaches]] and hunt for German U-boats. This strategy was deeply flawed because a U-boat, with its tiny silhouette, was always likely to spot the surface warships and submerge long before it was sighted. The carrier aircraft were little help; although they could spot submarines on the surface, at this stage of the war they had no adequate weapons to attack them, and any submarine found by an aircraft was long gone by the time surface warships arrived. The hunting group strategy proved a disaster within days. On 14 September 1939, Britain's most modern carrier, {{HMS|Ark Royal|91|6}}, narrowly avoided being sunk when three torpedoes from {{GS|U-39|1938|2}} exploded prematurely. ''U-39'' was forced to surface and scuttle by the escorting destroyers, becoming the first U-boat loss of the war. Another carrier, {{HMS|Courageous|50|6}}, was sunk three days later by {{GS|U-29|1936|2}}.

German success in sinking ''Courageous'' was surpassed a month later when [[Günther Prien]] in {{GS|U-47|1938|2}} penetrated the British base at [[Scapa Flow]] and sank the old battleship {{HMS|Royal Oak|08|6}} at anchor,{{Efn|He repeated a Great War feat by {{SMU|U-18|Germany|2}}.}} immediately becoming a hero in Germany.

[[File:Graf Spee scuttled.png|thumb|''Admiral Graf Spee'' shortly after her scuttling|left]]

In the South Atlantic, British forces were stretched by the cruise of ''Admiral Graf Spee'', which sank nine merchant ships of {{GRT|50000|disp=long}} in the South Atlantic and Indian Ocean during the first three months of war. The British and French formed hunting groups including three&nbsp;[[battlecruiser]]s, three&nbsp;aircraft carriers, and 15&nbsp;cruisers to seek the raider and her sister ''Deutschland'', which was operating in the North Atlantic. These hunting groups had no success until ''Admiral Graf Spee'' was [[Battle of the River Plate|caught off the mouth of the River Plate]] between Argentina and Uruguay by an inferior British force. After suffering damage in the subsequent action, she took shelter in neutral [[Montevideo]] harbour and was [[Scuttling|scuttled]] on 17 December 1939.

After this initial burst of activity, the Atlantic campaign quietened down. Admiral [[Karl Dönitz]], commander of the U-boat fleet, had planned a maximum submarine effort for the first month of the war, with almost all the available U-boats out on patrol in September. That level of deployment could not be sustained; the boats needed to return to harbour to refuel, re-arm, re-stock supplies, and refit. The harsh winter of 1939–40, which froze over many of the Baltic ports, seriously hampered the German offensive by trapping several new U-boats in the ice. [[Adolf Hitler|Hitler's]] plans to invade Norway and Denmark in early 1940 led to the withdrawal of the fleet's surface warships and most of the ocean-going U-boats for fleet operations in [[Operation Weserübung]].

The resulting [[Norwegian campaign]] revealed serious flaws in the German U-boat [[torpedo]]es: both the impact pistol and the [[magnetic pistol|magnetic influence pistol]] (detonation mechanism) were defective, and the torpedoes did not run at the proper depth, often undershooting targets. Only one British warship was sunk by U-boats in more than 38&nbsp;attacks. As the news spread through the U-boat fleet, it began to [[demoralization (military)|undermine morale]].{{Sfn|Bekker|1971|p=116-130}} Since the effectiveness of the magnetic pistol was already reduced by the [[degaussing]] of Allied ships, Dönitz decided to use new contact pistols, which were copied from British torpedoes found in the captured British submarine {{HMS|Seal|N37|6}}.{{Sfn|Blair|1996a|pp=158-160}} The depth setting mechanism was improved but only in January 1942 were the last complications with that mechanism discovered and fixed, making the torpedo more reliable.{{Sfn|Williamson|2010|p=43}}{{Sfn|Blair|1996a|p=485}}