Meanwhile they photographed each other patting pet dogs, playing cards, and relaxing in deck chairs on neatly trimmed grass. In 1940 there was honey still for tea, in this the world's last romantic battle.

To get to 11 Group's sector airfields ringed round London, Kesselring often routed one raid direct and another along the great blind spot created by the Thames Estuary. In the small hours of Sunday 25 August a night raid used the Estuary route to the oil tanks at Thameshaven. The crew of one aircraft lost their way, continued too far westwards, and dropped their bombs. They hit the City of London. The raid caused more dismay among the British War Cabinet and the staff of Air Fleet 2 than among the Londoners. The outer suburbs had already been bombed and Londoners had been expecting raids. The bomb-load of just one errant bomber was a gentle introduction to total war.

Just as the Rotterdam bombing prompted the 15 May War Cabinet to send the RAF to bomb the Ruhr next day, so now did Churchill authorize an immediate reprisal raid upon Berlin. During this period RAF Bomber Command believed themselves to be "reducing the scale of German attack by bombing aircraft assembly plants." Now eighty-one RAF bombers departed for Berlin on the night of Sunday 25 August. More civilians died. Here bombs were unexpected: the Nazi leaders had promised that Berlin was inviolable. They vowed to avenge the "atrocities". So began a chain of incidents that eventually ended not only the Battle of Britain, but — at Hiroshima — the war.

The German fighter formations had returned to the practice of flying well above the bombers. A Fighter Command Intelligence Summary of 30 August reported that fighters had been keeping to altitudes between 25,000 and 20,000 feet while the bombers were usually at 13,000 feet, with certain German units coming down to bomb at 4,000 feet.

For new pilots the high-altitude battles could be a frightening experience. It was very, very cold at 25,000 feet, and the Spitfires slipped and skidded through the thin air, as the propeller blades failed to bite. Invariably the Perspex misted over and reduced visibility. Only slowly did the aircraft add a few hundred feet, and for this reason the throttles remained wide open. It meant that if a pilot dropped back from his formation through lack of flying skill, he could never catch up with them again. And above them were the Bf 109s, watching and waiting for just such a straggler. This was the way that many young men died: alone and cold in the thin blue air, peering through the condensation into the glare of the sun, unable to see the men who killed them.

As a way of confusing the ground Observers, the Germans were now splitting the formations as they crossed the coast. This meant that Observer Corps reports were sometimes difficult to reconcile with the radar plots. Park ordered that his formation leaders should report the details of any enemy formation they saw, to help the Controllers form an accurate picture of what was happening.

But the uncertain weather of August brought more trouble to the Luftwaffe than to the British. If the raiders flew under the clouds they were visible to anyone who looked up. If they flew over them they were visible to fighters flying above. If they flew in the clouds it was dangerous, and they were unable to get the visual references they needed both for dead-reckoning navigation and for bombing the target.

And yet the defences could no longer be certain that the Luftwaffe depended upon dead-reckoning navigation. During the summer of 1940 there had been a second Battle of Britain in progress. It was fought by night fighters which each night sought, and usually failed to find, let alone shoot at, the lone night bombers that were ranging over southern England.

None of the senior British commanders and certainly not Dowding had any illusions about the chances of countering heavy forces of night bombers. In fact, there was a certain grim irony to their present predicament; they were engaged in a desperate race against time to find ways of countering the night bomber, and yet the more successful they were by day, the sooner would come the night attacks for which they were not yet ready.

It was June when the British first guessed at the sort of precision attacks that the Luftwaffe might be able to stage. A specially equipped RAF Avro Anson reconnaissance aircraft had found, in the night air above England, a mysterious beam that was only about 450 yards wide, and had all the characteristics of the Lorenz blind-landing system's beam.

It was this latter characteristic that was most worrying for the defences, for it implied rightly that any of the enemy bombers could be guided to their target by this system, without additional equipment. Examination of downed German bombers confirmed that the standard Lorenz equipment was suitable and sensitive enough for it, and by now intelligence officers, examining documents taken from German air crew, had come across references to such a device. It was code-named Knickebein (literally, dog-leg or bent-leg).

Investigating the beams drove the British to desperate measures. Listening Service men were sent to the tops of the tall radar towers. And a special RAF (No. 80) wing was created to counter Knickebein, which the British code-named "Headache."

Old Lorenz blind-landing sets were hunted up, and so was electro-diathermy equipment from hospitals. Both kinds of machinery were adapted into transmitters for jamming the German beams. By September jammers called 'Aspirins' were at work each night transmitting dashes that made it difficult for the German pilots to distinguish dots and dashes from their own transmitters (which worked on the basis of most blind-landing systems: dots mean too far left, dashes mean too far right, continuous note means you are on the correct course).

The difficulty with such counter-measures was measuring how successful they were. Bombers came wandering across darkened landscape (upon which towns, furnaces, and lighted factories could usually be seen if not recognized) and dropped bombs. How could anyone guess how near the enemy aviators had come to fulfilling their orders?

Most of these night raiders came from Hugo Sperrle's Air Fleet 3. With all his Bf 109s moved to the Pas de Calais, night raids had become largely his responsibility. He had been ordered to prepare a series of such attacks against Liverpool. After dark on 28 August the raids began and continued for four nights. Five Blenheim night-fighter squadrons using their airborne radar sets went on patrol but no enemy aircraft were shot down. Only one Blenheim crew — it was an aircraft from 600 Squadron — saw a German bomber but it was too slow to catch it.

The British counter-measures were certainly evident to Hugo Sperrle, whose crews were coming back baffled by the electronic jamming. German air crew talked about bombers which had gone in circles until the crew were dizzy. At least one Heinkel landed in England on the beach near Bridport believing that the jamming signal was their own guidance beam. The British did everything to spread the word about the effectiveness of the jamming. They succeeded only too well; even nowadays (nonsensical) stories are told about how the British bent the beams to cause the Luftwaffe to bomb Dublin, a neutral city.

Meanwhile 150 bombers delivered to Liverpool the heaviest attack so far suffered by any British target. Considerable damage was done to the docks and there were 470 casualties. Moreover, Sperrle's bombers did not have to depend solely upon the Knickebein apparatus.

Since 17 August a special unit—Kampfgruppe 100—had been transferred from Kesselring's command to Sperrle's. This Heinkel He 111 Gruppe was fitted with guidance equipment far beyond the limitation of the Knickebein beam. The X-Gerдt (fitted only to these aircraft with specially trained crews) provided a beam down which to fly and a series of three cross-beams. The accuracy of X-Gerдt was calculated as 120 yards, and as the highly skilled men of KGr 100 led long streams of bombers to Liverpool, there was no British counter-measure. For the time being, the British night sky belonged to the Germans.