The Opening Campaigns

The opening period of the European war moved between very different theatres and military problems. Poland was attacked from west, north, south and then east. Finland fought the Soviet Union in terrain and winter conditions unlike the campaigns farther south. Norway turned control of ports, sea lanes and airfields into the centre of the war. France was decided by a rapid operational penetration whose consequences reached the Channel before the Allied command could reconstruct a continuous front.

Britain then presented a different obstacle. A cross-Channel invasion required air superiority, and Directive 16 of 16 July 1940 made the defeat of the RAF a condition of the landing; Operation Sea Lion was postponed on 17 September with Fighter Command still operating. In spring 1941 the war shifted again to Yugoslavia, Greece and Crete, where political collapse, mountain routes, expeditionary forces, naval evacuation and airborne assault produced another set of problems.

Organised resistance on Crete ended on 1 June 1941. Three weeks later, on 22 June, Germany opened Operation Barbarossa, which changed the scale and direction of the continental war; from that point the Eastern Front becomes its own theatre, while the Mediterranean, Atlantic and occupation wars develop on separate tracks.

The German-Soviet pact of 23 August 1939 joined the first two campaigns. Its secret protocol gave the Soviet Union eastern Poland, Finland, Estonia and Latvia as a sphere of interest, and Moscow acted on it twice: it invaded Poland on 17 September and attacked Finland on 30 November. Finland's resistance drew attention in London and Paris, where the question of aid became tied to a second aim, cutting the iron-ore route through Narvik. The two governments scheduled the mining of Norwegian waters for 8 April 1940. Germany struck first, on 9 April.

Norway cost the Kriegsmarine a heavy cruiser, two light cruisers and about half of its destroyers. When planning for an invasion of Britain began in July 1940, the navy that would have to protect the crossing had few surface ships left. Air superiority became the condition for the landing, and the Battle of Britain, which the Royal Air Force dates from 10 July to 31 October, followed the fall of France.

In December 1940 Hitler's directives pointed two ways at once. Directive 20 of 13 December ordered preparations to occupy the northern Aegean coast and, if necessary, the whole Greek mainland; Directive 21, five days later, ordered preparations for an attack on the Soviet Union. British and Commonwealth troops began landing in Greece on 2 March 1941, and the coup in Belgrade on 27 March brought Yugoslavia into the German offensive. Greece fell in April, and Directive 28 of 25 April ordered the airborne attack on Crete. The defenders met three different problems: a Yugoslav army strung along some 3,000 kilometres of frontier, Greek and Commonwealth troops holding mountain passes, and a mixed garrison on an island that could be reached only by sea or air.

The campaigns rest on two kinds of record. The German directives and operational files in the Bundesarchiv show what the High Command ordered and when; Directive 28, which launched the attack on Crete, is filed there as RW 4/531. The British official histories, Derry on Norway in 1952, Ellis on France and Flanders in 1953 and Playfair on the Mediterranean in 1956, were written from the official records and show what commanders knew at the time. The Air Historical Branch narratives do the same for the RAF in France and the Battle of Britain, and the National Archives of Finland has digitised the war diaries of the Winter War.

German wartime descriptions often emphasised speed and collapse, and a campaign read only from them looks smoother than it was. The archives of the defending states keep the friction: mobilisation problems, local resistance, withdrawals and the political consequences that continued after the front moved on. The Yugoslav army was still mobilising along a frontier of some 3,000 kilometres when the attack came. The garrisons of the Metaxas Line held their forts for four days. The Polish government left the country on 17 September and carried on from abroad.