May, 1940. The German army has overrun France and the British Royal Air Force is evacuating its aircraft and pilots. A squadron of Hawker Hurricanes is quickly refueled and flown off ahead of the advancing Germans. Just as the ground personnel are torching the unflyable aircraft, a squadron of German ME-109s screams in at treetop level and shoots up the airfield.Back in Britain, Air Marshal Sir Hugh Dowding (Sir Laurence Olivier) recommends to Prime Minister Churchill that no further British fighter aircraft be risked in the defense of France. The British army is already being evacuated from the beaches of Dunkirk. The precious fighter planes will be needed for the defense of Britain. In conquered France, a large group of German HE-111 bombers is drawn up around a former French airfield, ready to deploy against the British Isles.A German diplomat, Baron Max von Richter (Curt Jurgens) makes an arrogant overture to British ambassador Sir David Kelly (Ralph Richardson) in neutral Switzerland. If the isolated British agree to allow Hitler a free hand in continental Europe, Germany will not use the Luftwaffe to flatten British cities in preparation for an invasion. The high-handed German receives an icy reception from the ambassador.At an RAF airfield in southeastern England, green pilots are hurriedly trained. A crusty RAF officer known only as 'Skipper' (Robert Shaw) takes one of his fledgling pilots up for special attention in the new Spitfire. The RAF begins to organize the coastal fighter defenses against the expected German air assault. They are counting heavily on the ability of the new coastal radar towers to provide early warning of incoming German air raids. Even with the assistance of radar, the German numerical advantage means that British pilots must shoot down German planes at the rate of four to one.RAF Squadron Leader Colin Harvey (Christopher Plummer), who is being transferred to Scotland, drives into town to meet his WAAF wife Maggie (Susannah York) at an inn. There is tension in the marriage. He wants her to apply for a posting in Scotland, but she resists. At the nearby airfield, there is a surprise visit from irascible Air Vice Marshal Keith Park (Trevor Howard). He admonishes new Squadron Leader Canfield (Michael Caine) that his pilots must be prepared to go up and meet the enemy with only two minutes warning.In contrast to the hard-pressed British, the victorious Germans are supremely confident and cocky. Invasion barges are being transported to the Channel Coast. On August 10, the Luftwaffe launches Operation 'Adlertag' (Eagle Day), a massive strike against British radar sites and airfields near the coast. HE-111 bombers and ME-109 fighters roar from their French airfields. The attack is preceded by JU-87 Stuka dive bombers, dropping their payloads on the troublesome British radar towers. The vulnerable Stukas are soon set upon by British Spitfires, who make short work of them. Close behind the dive bombers, more than 100 Heinkel HE-111s cross the British coastline, escorted by ME-109 fighters. The British airfields are soon under heavy attack, as the pilots scramble to get their Hurricanes and Spitfires airborne. The British inflict aircraft losses on the Germans at a three-to-one rate, but the airfields are heavily damaged. After the attack, RAF Group Captain Baker (Kenneth More) surveys the damage to his own airfield. The British ruefully acknowledge that the German strategy of attacking their airfields is working.In an attempt to overwhelm the British defenses, the Germans mount simultaneous raids against southeastern England (from France) and northern England (from Norway). However, the bomber formations from Norway must proceed without fighter escort. Squadron Leader Harvey's fast Spitfires take a horrendous toll on the lumbering HE-111 bombers, shooting down 23 without loss. Yet the pilot and aircraft attrition rate is still working against the British.Adding to the RAF's problems is a personal verbal battle between the commanding officers of 11 Group, Keith Park (Trevor Howard), and 12 Group, Trafford Leigh-Mallory (Patrick Wymark). 12 Group is tasked with protecting 11 Group's airfields while 11 Group meets the enemy, but in raid after raid 12 Group aircraft are nowhere to be seen. Called to meet Dowding, Leigh-Mallory explains that the "Big Wing" tactic takes time for form up, while Park complains that the tactic simply is not working. Dowding ends the debate noting a critical shortage of pilots, wearily remarking, "We're fighting for survival, and losing."Just as Squadron Leader Harvey and his wife Maggie rendezvous at a swank London hotel, wayward German bombers accidentally drop the first bombs on the city, but they both survive. Hitler had previously avoided targeting London in hopes of avoiding the remorseless total war that would surely follow. In retaliation, the British stage their first air raids on Berlin. Though the damage is negligible, an enraged Adolf Hitler publicly orders London to be razed. Hermann Göring (Hein Riess) arrives in France to personally command the attack, confident that the end of the battle nears. Their first attack skirts the RAF, who are still defending their airfields to the south, and they bomb unopposed. Night time attacks follow and London burns.Meanwhile, to supplement Commonwealth forces, the RAF has been forming units of foreign pilots who have escaped German-occupied countries; the main difficulty is their lack of English-language skills. While on a training flight, a Free Polish squadron accidentally runs into an unescorted flight of German bombers. Ignoring the commands of their British training officer, they peel off one by one and shoot down several of the bombers with unorthodox aggressive tactics. Park rewards them by elevating them to operational status, leading Dowding to do the same for the Canadian and Czech squadrons as well.While discussing the day's events, Park and Dowding examine the German switch to London. Given a respite, Park notes that he will be able to repair his airfields and bring his squadrons back to full strength. Dowding adds that 12 Group units north of London are now all within range, while enemy fighters are at the extreme edge of their own range. He concludes that "turning on London could be the German's biggest blunder."The next German daytime raid is met by a massive response; watching his formations build up in 11 Group's operations room, Wing Commander Willoughby (Robert Flemyng) wryly states "this should give them something to think about." RAF fighters arranged into large groups, attack en masse, overwhelming the German raids. Göring is incensed, ordering his fighters remain with the bombers, an order the pilots hate. Losses continue to mount on both sides.The desperate struggle reaches a crescendo on September 15, 1940 (the Battle of Brittan Day). The Luftwaffe launches wave after wave of bombers and fighters against London. Winston Churchill is in attendance at 11 Group's operations room. In the underground bunker, British ground control personnel order every squadron into the air to meet the massive attack. Intense combat in the sky over London follows, with both sides taking heavy losses. The outcome is so confused that Dowding refuses to comment on the events to the local press. RAF pilots shoot down scores of German bombers against less than 30 British fighters lost.It is effectively the end of daylight raids against Britain, and having failed to subdue the RAF, Hitler cancels the invasion of England.The next day the RAF anxiously await a raid that never comes. Likewise the Luftwaffe is disheartened by heavy losses and also await orders that never come to resume raiding. Two German anti-aircraft gunners, who had earlier observed a French port teeming with Kriegsmarine vessels and landing barges, now observe a deserted harbour basin. Göring leaves the front by train to travel back to Berlin, accusing his commanders of betrayal.In the final shot, Dowding looks out over the gardens and up to the sky where the words of Winston Churchill appear onscreen: "Never in the field of human conflict was so much owed by so many to so few."The text also shows that approximately 350 British RAF pilots have given their lives in the Battle of Britain, as well as 100 more pilots from Australia, Canada, South Africa, Poland, Czechoslovakia and other Allied nations.