Shortly before noon on Wednesday 13 June 1917, Londoners did something that now seems unthinkable. They stepped out of offices, shops and tea rooms and looked up. A formation of big biplanes was sliding across a clear summer sky towards the City, and many people assumed they were British.

They were German Gotha G.IV bombers of Kagohl 3, and within minutes 72 bombs had fallen within a mile of Liverpool Street Station. At about 11.40 one more 50 kg bomb dropped through the roof of the Upper North Street School in Poplar, and the war in the air stopped being a spectacle.

The raid killed 162 people and injured 432, the deadliest single air raid on Britain of the First World War. Eighteen of the dead were children from that one school. Afterburner has already told the story of the Zeppelins that first bombed London and of the Zeppelin-Staaken Giants that came later. This is the story of the Gotha raids in between, and of how a classroom in the East End helped create the Royal Air Force.

Kagohl 3: The England Squadron

By late 1916 the Zeppelin campaign was faltering. Airships were huge and slow, and once British fighters carried incendiary ammunition they burned with terrifying ease. The German army turned to aeroplanes and planned Operation Türkenkreuz (Turk's Cross), a daylight bombing offensive against England.

The weapon was Kampfgeschwader der Obersten Heeresleitung 3, or Kagohl 3, soon nicknamed the England Geschwader. Hauptmann Ernst Brandenburg took command in March 1917. His crews flew from airfields around Ghent in occupied Belgium, among them St Denis-Westrem and Gontrode, well back from the front line.

Their aircraft was the Gotha G.IV, a three-seat biplane with two 260 hp Mercedes D.IVa engines driving pusher propellers. It carried up to 500 kg of bombs, had a service ceiling of about 5,000 metres and could stay aloft for six hours, though its top speed was only 135 km/h. Its clever feature was the “Gotha tunnel”, a trough through the rear fuselage that let the rear gunner fire down and backwards at fighters creeping up from below.

Folkestone: The Dress Rehearsal

The first attempt came on 25 May 1917. More than 20 Gothas set out for London, but thick low cloud over the capital forced them to turn away over Kent. They followed the railway line to Folkestone, where the streets were full of people shopping on a fine Friday evening before a bank holiday weekend.

In Tontine Street a single bomb exploded among a queue outside a greengrocer's shop. With the bombs that fell on the Canadian army camp at Shorncliffe, the raid killed about 95 people and injured nearly 200. British fighters climbed after the raiders, but most were obsolete types that simply could not reach the Gothas' height.

Mark Felton tells the story of the England Geschwader and its Gotha G.IV bombers, the start of what historians call the first Blitz.

Wednesday Morning Over the City

After a raid on 5 June was diverted to Sheerness, the Gothas came back on 13 June. Twenty took off from the Ghent airfields. Two turned back with engine trouble and a few others peeled off to bomb Margate and Shoeburyness, leaving 14 to press on to London.

There was no public warning system. Three bombs hit Liverpool Street Station, where 16 people died. Others fell on Fenchurch Street, Aldgate and the Royal Mint. In Central Street, PC Alfred Smith pushed a group of factory workers back indoors moments before a bomb burst in the road and killed him.

More than 90 British aircraft went up, but few could climb high enough to engage. In a Bristol F.2 Fighter over Ilford, the observer, Captain C. H. C. Keevil, was killed by return fire. Not a single Gotha was lost. At the inquests that followed, the coroners spoke for a city in shock.

The Classroom in Poplar

As the formation turned for home over the East End, crews released what they had left. A 50 kg bomb struck the three-storey Upper North Street School, crashed through the girls' and boys' floors and exploded in the infants' department on the ground floor, where 64 small children sat in two classes.

Eighteen children died, most of them five or six years old. One girl, Rose Symmons, was pulled alive from the rubble three days later; her twelve-year-old brother Jimmy had refused to stop searching. A teacher, Mrs Middleton, was injured but stayed on to show rescuers where children might be found.

The funeral on 20 June became a focus of grief and anger. Thousands lined the East India Dock Road, more than 600 wreaths arrived and a personal message from King George V and Queen Mary was read out. Fifteen of the children were buried together in a communal grave at East London Cemetery.

Local people collected around £1,500 door to door for a memorial, unveiled in Poplar Recreation Ground on 23 June 1919. One of the last victims was the school caretaker, Mr Batt, who had recovered his own son's body from the building. He died that November.

Anger on the Ground

In Germany the raid was hailed as a triumph, and Brandenburg went to receive the Pour le Mérite. On the return flight his aircraft crashed on take-off. His pilot, Oberleutnant Hans Ulrich von Trotha, was killed and Brandenburg lost a leg. Hauptmann Rudolf Kleine took over the squadron on 23 June.

Kleine led 22 Gothas back to London on 7 July, and more than 50 people died. British pilots flew around 100 sorties against the formation and brought down one bomber. According to the RAF Museum, mobs attacked shops and people with German-sounding names. On 17 July the King renamed the royal house Windsor, dropping Saxe-Coburg and Gotha, a German name shared with the town where the bombers were built.

Parliament was furious that London still had no air raid warnings. When asked about schools, the Home Secretary, Sir George Cave, said it would not be practicable to post a constable at each of the 2,400 schools in the Metropolitan Police district. Prime Minister David Lloyd George turned to Jan Smuts, the South African general in his War Cabinet.

A scene from HISTORY's series WWI: The First Modern War showing Germany introducing its new bombers against London.

Into the Dark

Smuts delivered his first report in little more than a week. It led to the London Air Defence Area under Major-General Edward Ashmore, which put guns, fighter squadrons and observers under one command, with better aircraft brought back from France. Air raid warnings were finally approved. On 22 August, Gothas sent against Margate and Dover lost three of their number.

Kagohl 3 switched to night bombing. Its first night raid, on Chatham on 3 September, killed about 130 sailors sleeping in a drill hall. From late September the Gothas were joined by the four-engined Giants of Rfa 501, and up to 300,000 Londoners sought shelter in Underground stations.

Night raids were harder to stop but also harder to fly, and many damaged Gothas crashed on landing back in Belgium. The newer Gotha G.V proved no better than the G.IV. Kleine was shot down and killed near Ypres on 12 December 1917, and a recovered Brandenburg took back command that day. In January 1918 two Sopwith Camel pilots scored the first night-fighter victory over a heavier-than-air bomber above Britain.

The Report That Made the RAF

Britain's air power was still split between two services: the Royal Flying Corps belonged to the army and the Royal Naval Air Service to the navy. Their rival demands for aircraft and engines had defeated every attempt at coordination.

Smuts's second report, submitted on 17 August 1917, proposed the answer: one air service with its own ministry and staff. It also looked far beyond London's defences.

The Air Force (Constitution) Act became law on 29 November 1917, and on 1 April 1918 the two services merged into the RAF. Seven weeks later, on the night of 19/20 May 1918, 38 Gothas and three Giants set out against London in the largest raid of the war. Six Gothas were shot down and a seventh forced down. It was the last aeroplane raid on Britain.

Across 52 raids, German aeroplanes killed 857 people in Britain. The 1917 defence system grew into the network that fought the Battle of Britain, and the RAF exists because Gothas once flew over London in daylight. In Poplar, a stone angel still stands over the names of eighteen children.

HistoryPod's short account of 13 June 1917, London's deadliest air raid of the First World War.

Sources: Wikipedia (German bombing of Britain, 1914–1918; Gotha G.IV; Mayflower Primary School, Poplar; London Air Defence Area), Ian Castle, RAF Museum, The National Archives (History of Government blog), Historic England, Western Front Association, Air & Space Forces Magazine