From September 1940 onwards, Göring’s daylight offensive against RAF Fighter Command continued on a gradually reducing scale, with heavy bomber attacks giving way to raids by escorted fighter-bombers. During the same period, attempts to reduce the morale of the civilian population and force the British Government to surrender were made through the medium of heavy raids on London followed by a maximum-effort nocturnal assault on the capital. In November, this assault was expanded to other British cities and centres of industry, alternating between deliberate attempts to wreck civil morale and carefully planned attacks on Britain’s supply and production centres. These phases of the German night bombe offensive, beginning with the raid on London on 7 September and dragging on through the winter to cease finally in May 1941, became known in Britain as the Blitz.
The main reasons why the Luftwaffe turned to night attacks lay in the alarming rate of attrition suffered by the Kampfgruppen in their attacks by day. Within the RAF at this time night fighting techniques relying on visual contact assisted by searchlights and the well-proven GCI system achieved few successes. Until the availability of efficient Airborne Interception (AI) radar, the German night bomber was to come and go with little hindrance. The first operational radar set, the AI Mk IV, was about to enter service but only on a very limited scale and was still highly experimental.
The adoption of night bombing also presented problems to the Luftwaffe. There were those of accurate night navigation and bombing, and these were compounded by an overall reduction in efficiency of bomber crews owing to the massive loss of experienced men during the Battle of Britain. The Germans, however, considered that any deficiencies in night operational training would be compensated by the use of radio aids to navigation that were in the hands of a few specialised bomber units. The Germans had been far ahead of any other combatant power in the design and development of such aids, but by using the various types of equipment prematurely they allowed their secrets to be compromised and effective jamming by the enemy to be initiated. To summarise, the three principal aids to blind-bombing and navigation then in use were as follows:
- ‘Knickebein’ (Bent Leg): This relatively unsophisticated equipment could be used by bombers equipped with the Lorenz blind-approach aid. The pilot flew his aircraft along an approach radio beam to the target, the bomb aimer releasing his bombs on receipt of a second radio signal beamed to traverse the approach beam at a particular point. The aid was easily jammed and could even be ‘bent’, and its only advantage lay in its ability to be used by a considerable number of aircraft.
- X-Gerät (X-Equipment): Specialised aid to blind-bombing installed only in the He 111H-4s of Kampfgruppe 100 (Maj. Friedrich Aschenbrenner) operating from Vannes and Chartres. It consisted of one approach beam traversed in the vicinity of the target of three others. When the pilot received the first signal 31 miles (50km) short of the target, he lined up accurately on the approach beam, compensating for drift. The second and third signals occurred at 12 miles (20km) and 3 miles (5km) respectively. A computer calculated the aircraft’s groundspeed and utilising this information automatic bomb release followed pressing a button on receipt of the third signal. X-Gerät was very accurate but could be effectively jammed.
- Y-Gerät (Y-Equipment): Specialised aid installed only in the He 111H-4s of III/KG 26 (Maj. Victor von Lossberg) based at Poix-Nord. Once again an accurate target approach beam was used, but in this case bomb release was made at an accurately-measured range along the beam. This range was computed automatically by the associated ground radar station. The station sent an interrogator pulse. After a set interval special equipment in the bomber returned an answering pulse. Range was then deduced by the time signal (a matter of milli-seconds). At the correct range, the ground station relayed a bomb release signal. Y-Gerät was another very accurate system but again one that could be jammed effectively.
The night blitz, 7 September–31 May 1941
The Kampfgruppen engaged in the Blitz comprised the same units that had participated in the Battle of Britain under Luftflotten 2, 3 and 5, with the addition of some 90 bombers that had been held in Germany. Some 1,300 bombers were available for operations, but low serviceability kept the maximum effective strength to about 700 of these. After the mass daylight attack on London docks on 7 September, raids by 60 to 260 bombers took place after dusk during every night of the month. The effective jamming of Knickebein by No. 80 Signals Wing of the RAF rendered this equipment useless and throughout October the Luftwaffe had to make use of bright moonlight for navigation and bombing. During the early part of that month, London suffered a nightly assault by an average of 200 bombers. On 9 October, the Luftflotten were ordered to increase the effort, and that night London received 386 tons of HE and some 70,000 1-kg incendiary bombs in the course of 487 bomber sorties: on succeeding nights the attack was repeated by forces mounting 307, 150, 303 and 320 sorties. The Germans anticipated that the civil population would panic and force a surrender, but they, and in turn the Allies, underestimated the resilience of civilian morale in the face of indiscriminate heavy bombing.
Early in November, Göring decided to extend the Luftwaffe effort to a long-term attrition against the whole British industrial effort. Parallel with this new plan came the decision to use KGr 100 and the X-Gerät system as target finders. On locating the target KGr 100 was to drop incendiary bombs as target-markers for the follow-up force of bombers. The new plan as set out for the Luftflotten by Göring was as shown in the accompanying table.
On the night of 14/15 November, the target was Coventry. Using X-Gerät, twelve He 111s of KGr 100 crossed Lyme Bay, Dorset, at 18.17hrs heading north-east. At 20.15hrs, the Gruppe dropped over 1,000 incendiaries on the city starting numerous conflagrations, and as they droned away into the clear night, three separate bomber streams converged on Coventry from the Wash, Dungeness and Portland. Throughout the night successive waves of KG 1, KG 26, KG 27, KG 55, LG 1 and Kü.Fl.Gr 606 flew in to add to the devastation, and in the course of 469 sorties, the Luftwaffe delivered 394 tons of HE bombs, 56 tons of incendiaries and 127 parachute LMB 5 sea-mines; the latter caused considerable blast damage. Air defences were minimal and most of the bombers returned to base unscathed.
Birmingham came under heavy attack on the night of 19 November. Once again the now-established pattern was followed, with KGr 100 leading KG 26, KG 54, KG 55 and Kü.Fl. Gr 606. This time five bombers were brought down by the defences, one, a Ju 88A-4, was shot down over Dorset by Flt. Lt. J. Cunningham and Sgt. J. Phillipson, flying a Beaufighter IF of No. 604 Squadron and using the new AI Mk IV radar. This was the first radar kill of the war, but many months of experiment and disappointment lay ahead for the RAF night-fighter crews before their airborne radar equipment was to bring consistent results. The onus of night fighting still lay on Hurricane, Defiants and Blenheims, their crews relying on visual contact to achieve indifferent success. The Birmingham attack was followed during the remainder of that month and December by a succession of large-scale raids on London, Bristol, Plymouth, Liverpool, Southampton and Sheffield.
The year closed with a sharp attack on London in the evening of 29 December 1940. The raid was abandoned by the Luftwaffe some two hours after its commencement owing to deteriorating weather conditions. Only about 130 bomber sorties were mounted in the event, all aircraft carrying incendiaries, but by the time the weather closed in after 22.00hrs, the City of London was suffering its worst ordeal by fire since the Great Fire of 1666! Contrary to belief, this attack was a routine one and not a deliberate attack to wreck the City. That evening, the X-Gerät approach beam was actually laid in a SE–NW direction over the Charing Cross and Tottenham Court Roads. A fresh wind was blowing from the south-west and insufficient allowance for this wind was made by KGr 100 whose incendiaries fell about one mile to the East and immediately to the North-West of St Paul’s Cathedral. The aircraft of the main bomber force, seeing the resultant fires, contributed their loads of HE and incendiaries.
In January 1941, the Luftwaffe still maintained a considerable force of bombers in the West: Fliegerkorps I, IV and V mustered 26 Kampfgruppen based in France and Belgium for attacks on Great Britain. By this time, however, a general lack of confidence in the blind-bombing aids was apparent, owing primarily to British mastery of the X-Gerät and to the widespread use of decoy fires. The Kampfgruppen turned once again to moonlight raids, concentrating on British seaports over which minimum interference to the radio beams could be expected. Accordingly ports such as Plymouth, Bristol, Swansea, Cardiff and Hull came under night attack.
In April, the German campaigns in the Balkans and Greece were already underway. Several fighter, dive-bomber and reconnaissance units had been detached from Luftflotte 3 in Northern France and deployed to the south during the winter and early spring. The anti-shipping force, Fliegerkorps X, had been transferred from Norway to the Mediterranean at the end of 1940. During May 1941, Luftflotte 2 left France for the East, along with KG 1, KG 27, KG 51, KG 54, KG 55, KG 76, KG 77 and I/LG 1. The moves were made under a cloak of secrecy, and as a cover to these movements, bomber raids on Britain were accompanied by false radio traffic to simulate larger forces. To maintain the semblance of a large force in being, the Luftwaffe executed the heaviest raid of the entire Blitz against London on the night of 10 May, crews flying two and even three sorties and 708 tons of HE and 87,000 incendiaries were dropped, causing great damage to greater London in the course of 550 sorties. Three nights later the raid was repeated in similar strength.
By the end of May 1941, Kesselring had moved with the whole of Luftflotte 2, along with the bomber units of FlKps IV and V, to the attack on the Soviet Union, leaving in the West the anti-shipping units of Fliegerkorps IX and Fliegerführer Atlantik, and a mixed force of bombers and single-engined fighters under Luftflotte 3.
In time, these units were to be whittled away by the more important commitments in the Soviet Union and the Mediterranean, leaving only a small force of mine-laying and anti-shipping units in the West. The Blitz was over. The programme for the subjugation of Britain had overrun its time, and although a considerable damage had been wrought to British cities and industries, the time for the hoped-for collapse had passed. The Luftwaffe had had every opportunity to bring Britain to her knees but failed because there had been no firm and continuous policy of attack: a shortcoming compounded by the manifest unsuitability of much of the equipment of the Luftwaffe for the task with which the service had been presented. Lack of coherent policy from OKL had all too frequently allowed hard-pressed cities to recover from large-scale raids where one more raid could have produced complete breakdown. The only solution now lay in the starving of Britain of food and supplies by air and sea attacks on her shipping, and awaiting or forcing surrender after the expected defeat of Russia in the autumn of 1941.