'Gomorrah' was the Allied air offensive against the German port city of Hamburg (24 July/3 August 1943).

A major city with great importance in the industrial and maritime industries, Hamburg was very heavily bombed on many occasions by the RAF and USAAF, and the most concentrated of these efforts was the series designated as 'Gomorrah'. At the time it represented the heaviest assault in the history of air warfare.

The Allies bombed Hamburg, a large port and industrial centre of strategic significance, very many times in World War II, and these attacks included both numerous strategic attacks and also large numbers of diversion and nuisance raids. Hamburg’s shipyards and U-boat pens, and the oil refineries of the Harburg area were attacked throughout the war.

The attack during the last week of July 1943 was 'Gomorrah', and created one of the largest firestorms raised by the RAF and USAAF in World War II, killing 42,600 civilians and wounding 37,000 in Hamburg and practically destroying the city. Before the attack there had been no rain for some time, rendering the city (especially its mediaeval wooden structures) tinder dry and therefore all the more vulnerable to devastating fire. The combination of unusually warm weather and good flying conditions meant that the bombing was highly concentrated around the intended targets, and also contributed signally to the creation of a vortex and whirling updraft of super-heated air which resulted in a tornado of fire some 1,500 ft (460 m) high, an effect which had been totally unexpected. Various other techniques and devices, some of which had been used before in an individual form, were now used together, and the combination of tight area bombing, accurate target marking by pathfinder bomber and H2S navigation and bombing radar also played a major part in boosting the efficiency of the bombing. 'Window', an early form of chaff, was successfully used for the first time by the RAF, the clouds of shredded tinfoil dropped by the pathfinders as well as the initial bomber stream producing millions of false echoes which saturated the German radar screens and made it impossible for controllers to supervise the anti-aircraft artillery and night-fighter defences effectively. As a result, the raids inflicted severe damage to German armaments production in Hamburg.

Until the decision to destroy Hamburg was taken, the primary objective of RAF Bomber Command had been the Ruhr industrial region, whose cities, factories and communication networks had been the target of a five-month campaign.

'Gomorrah', also known as the Battle of Hamburg, was a campaign of air raids beginning on 24 July and lasting for eight days and seven nights. The operation was originally formulated by Air Chief Marshal Sir Arthur Harris, commanding RAF Bomber Command, and took the form of a joint effort between Bomber Command, which included squadrons of the RAAF and RCAF, and Brigadier General Frederick L. Anderson’s VIII Bomber Command of what later became Major General Ira C. Eaker’s US 8^th AAF. These two forces co-ordinated their efforts into a 'round the clock' bombing assault in which the British attacked by night and the Americans by day.

The initial attack of 24/25 July included two innovations. These were 'Window' chaff to saturate German radar screens with vast numbers of false echoes and thereby confuse the German radar system, and the use of radio by the Pathfinder Force aircraft, which normally maintained a strict radio silence, to report the wind they encountered: the data of this wind reporting were processed and relayed to the bomber force navigators, who were thereby significantly aided in the accuracy of their bomb-aiming.

Harris signed the order for the operation on 27 May, and the operation began almost one month later. No. 35 Squadron led the target marking and as a result of the clear weather and the navigation accuracy provided by the H2S the pathfinders performed very well and their markers fell very close to the designated aiming point. At about 00.57 on 24 July the first bombs started to drop, and this initial RAF raid lasted almost one hour. In all, 791 bombers were committed to this first phase of 'Gomorrah', and of these 728 bombed for 50 minutes. Less than half the force bombed within 3 miles (4.8 km) of the city centre, and the almost inevitable bomb creepback was 6 miles (9.6 km). Damage was caused in the centre of the city and the north-western districts, particularly in Altona, Eimsbüttel and Hoheluft. The Rathaus (town hall), St Nikolai church, main police station, main telephone exchange and Hagenbeck Zoo were among the well-known landmarks which were hit. About 1,500 people were killed, and this was the largest death toll in any raid to date outside the range of the 'Oboe' radio navigation system which helped to concentrate the bombing pattern.

The use of 'Window' contributed to the fact that the British lost only 12 aircraft, or 1.5% of the force. While some 40,000 firemen were available to tackle fires, control of their resources was damaged when the telephone exchange caught fire and rubble blocked the passage of fire engines through the city streets; the fires were still burning three days later.

The British also flew a number of minor and diversionary raids: 13 Mosquito light bombers made nuisance attacks on Bremen, Kiel, Lübeck and Duisburg; six Vickers Wellington medium bombers laid lines in the Elbe river, and aircraft of operational training units also made a number of sorties. There were no British losses.

A second raid, this time by the day bombers of the VIII Bomber Command, started at 16.40 on 25 July. It had been intended that 300 US aircraft would attack Hamburg and Hanover, but problems with assembling the force in the air meant that Hamburg was reached by only 90 Boeing B-17 Flying Fortress heavy bombers of Colonel Claude E. Duncan’s 1^st Bombardment Wing (Heavy) with the 91^st, 351^st and 381^st Bombardment Groups, and Lieutenant Colonel Donald S. Graham’s 1^st Bombardment Wing (Heavy) with the 303^rd, 379^th and 384^th Bombardment Groups. The US bombers attacked the Blohm und Voss shipyard, U-boat facilities and an aero engine factory. German Flak damaged 78 aircraft. The shipyard area was not badly damaged and the aero engine factory could not be seen for smoke, though an electricity generating station was attacked instead of this.

de Havilland Mosquito light bombers of the RAF carried out nuisance raids to keep the city on a state of alert, and delayed-action 'Cookie' bombs from the night’s raid exploded at intervals and thus had much the same effect. Additional firefighters were brought in from other cities, including Hanover, and a result of this was that when 54 US heavy bombers attacked Hanover, many of its firefighters were unavailable and the fires in Hanover burned unchecked. Another 71 US bombers attacked the U-boat yards in Hamburg at about 12.00.

Another British attack on Hamburg for the night of 25/26 July was cancelled in recognition of the problems which would affect bombing accuracy as a result of the fact that Hamburg was wreathed in smoke, but six Mosquito light bombers did make a nuisance raid on Hamburg

Instead a force of some 705 bombers raided Essen, which was selected as a target in an attempt to achieve a good result against this major target while the effects of 'Window' were still fresh and the Germans had no counter. The raid was successful, with particular damage being recorded in the industrial areas of Essen’s eastern half. The Krupps works suffered what was probably their most damaging raid of the war, and on the following morning, Dr Gustav Krupp suffered a stroke from which he never recovered. Some 51 other industrial buildings were destroyed and 83 seriously damaged, 2,852 houses were destroyed, 500 persons were killed, 12 were missing and 1,208 were injured. The 500 dead were recorded as 165 civilian men, 118 women and 22 children, 22 servicemen, 131 foreign workers and 42 prisoners of war.

Minor operations at this time were undertaken by six Mosquito light bombers against Hamburg and three each against Köln and Gelsenkirchen, 17 aircraft to lay mines off the Frisian islands group, and seven operational training unit sorties. None of these undertakings suffered any loss.

A third raid was made during the early morning of 26 July, but starting at 00.20 this was extremely light as a result of a severe thunderstorm and high winds over the North Sea, leading many of the bombers to jettison the explosive part of their bomb loads (though retaining their incendiaries), and only two bomb drops were reported. The attack is often not counted when the total number of 'Gomorrah' attacks is reckoned.

There was no day raid on the 27 July.

On the night of 27/28 July, shortly before midnight, 739 out of 787 RAF aircraft attacked Hamburg. The unusually dry and warm weather, the concentration of the bombing in one area, and firefighting limitations resulting from the use of 'blockbuster' bombs early in the raid and the recall of Hanover’s firefighters to their own city culminated in the so-called Feuersturm (firestorm). Guided by Pathfinder Force aircraft equipped with H2S radar, the aircraft bombed about 2 miles (3.2 km) to the east of the city centre. Facilitated by the dry conditions, a firestorm was created in the working class districts of Hammerbrook, Hamm, Borgfelde and Rothenburgsort. The tornado-like fire created a huge inferno with winds of up to 150 mph (240 km/h) reaching temperatures of 815° C (1,500° F) and altitudes greater than 1,500 ft (460 m), incinerating more than 8 sq miles (20.7 km²) of the city. Asphalt streets burst into flame, and fuel oil from damaged and destroyed ships, barges and storage tanks spilled into the water of the canals and the harbour, causing them to ignite as well. Most of the deaths attributed to 'Gomorrah' happened on this night, and a large number of those killed died while they sought safety in bomb shelters and cellars: the firestorm consumed all the oxygen in the burning city above them. The furious winds created by the firestorm had the power to sweep people up off the streets like dry leaves, and it has been recorded that some people who tried to walk along were pulled into the fire.

The bombing was more concentrated than the RAF was usually able to manage at this stage of the war. It is estimated that in a little more than 30 minutes the bomb loads of some 550 to 600 bombers fell into an area measuring just 2 by 1 miles (3.2 by 1.6 km), and this gradually spread the fire to the east. The firestorm lasted for about three hours, consuming approximately 16,000 multi-storey apartment buildings and killing an estimated 30,000 people, most of them by carbon monoxide poisoning when all the oxygen was drawn out of their basement shelters. Fearing further raids, two-thirds of Hamburg’s population, about 1.2 million persons, fled the city in the aftermath.

On the night of 28/29 July a nuisance raid was flown by four Mosquito light bombers.

On the night of 29/30 July a major British raid involved 777 aircraft guided by H2S-equipped pathfinders. The plan was to approach Hamburg from almost due north ands to bomb the untouched northern and north-eastern suburbs. The pathfinder aircraft arrived more than 2 miles (3.2 km) too far to the east and marked an area just to the south of the devastated firestorm area. The main force bombing crept back about 4 miles (6.4 km), through the devastated area, but then produced very heavy bombing in the Wandsbek and Barmbek districts and parts of the Uhlenhorst and Winterhude districts, all of which were all residential areas. Some 707 aircraft dropped 2,318 tons of bombs, and though there were widespread areas of fire there was no firestorm. The worst incident was in the shelter of a large department store in Wandsbek: the building collapsed and blocked the exits from the shelter in the store’s basement, and 370 persons died, poisoned by carbon monoxide fumes from a nearby burning coke store. The British losses were 28 aircraft, 3.6% of the force despatched.

The night’s minor operations were four Mosquito light bombers to Düsseldorf, six Wellington medium bombers laying mines in the Elbe river, nine Lancaster heavy bombers of No. 617 Squadron dropping leaflets over Italian cities, and three operational training unit sorties. No British aircraft were lost.

A planned raid on 30/31 July was cancelled as a result of thunderstorms over the UK and North Sea.

On the night of 2/3 August 740 British aircraft were despatched against Hamburg, but the bombers flew into a large area of thunderstorms over Germany, and the raid was a failure. Many crews turned back early or bombed alternative targets. At least four and probably more aircraft were lost because of icing, turbulence or being struck by lightning. No pathfinder marking was possible at Hamburg, and only scattered bombing took place there. Many other towns in a 100-mile (160-km) swathe of northern Germany received a few bombs. A sizeable raid developed against the small town of Elmshorn, 12 miles (19.25 km) from Hamburg. It is believed that a flash of lightning set a house on fire, and bomber crews saw this through a gap in the storm clouds and started to bomb the fire. Some 254 dwellings were destroyed in Elmshorn and 57 people were killed, some of them refugees from recent raids on Hamburg. The British losses were 30 aircraft, constituting 3.6% of the force despatched.

The night’s minor operations included five Mosquito light bombers to Duisburg, six Wellington medium bombers minelaying in the Elbe river, and 12 operational training unit sorties. One Wellington minelayer was lost.

'Gomorrah' killed 42,600 people, left 37,000 wounded and caused about 1 million civilians to flee the city. The city’s labour force was reduced permanently by some 10%. The Allies had deployed about 3,000 aircraft and dropped, 9,000 tons of bombs. No later city raid shook Germany as greatly as did that on Hamburg, and documents reveal that German officials were thoroughly alarmed and there is some indication from later Allied interrogations of Nazi officials that Adolf Hitler stated that further raids of similar weight would force Germany out of the war. The industrial losses were severe, and Hamburg did not recover to full production except in the essential armaments industries, where a maximum effort was made.German figures indicate that 183 of 524 large factories were destroyed, and 4,118 of 9,068 smaller factories. Other losses included damage to or destruction of 580 industrial concerns and armaments works, 299 of which were important enough to be listed by name. Local transport systems were completely disrupted and did not return to normal for some time. Some 214,350 or 414,500 dwellings were destroyed.

Hamburg was hit by air raids another 69 times before the end of World War II.