April 26 is the 70th anniversary of the destruction by bombing of the Basque city of Guernica during the Spanish Civil War. Notwithstanding far greater loss of life inflicted by subsequent air raids launched during the Second World War, Guernica has become symbolic of the horrors of air power when unleashed on the defenceless citizens of an unprotected city.

The atrocious nature of the event was recognised at the time, notably in the graphically indignant reports made for The Times, by George Steer, the paper’s man on the spot. It was immortalised in the same year by Picasso, whose picture Guernica, symbolises for all time not just the city’s grief, but the suffering that mankind persists in heaping upon itself.

In 1937, with the Spanish Civil War raging with unabated savagery, Euskadi — the Basque country — was still holding out against the attacks of Franco’s rebel Nationalist troops. The ancient town of Guernica, high in the remote hills of the coastal province of Vizcaya, was an unmilitarised and undefended community. At its centre was was an oak tree where the traditional liberties of the Basque people were periodically affirmed. Guernica and its 5,000 inhabitants had no conceivable strategic significance and had seen little of the effects of the conflict.

This was to change when General Emilio Mola, commander of the Nationalist Army of the North vowed “to end the war in the North of Spain quickly”. Guernica was selected as the object of the most massive air attack that could be delivered by the forces at Mola’s disposal. Though nominally under his control, these consisted of the crack German squadrons of the Condor Legion supported by some Italian aircraft of the Corpo Truppe Volontarie. The raid on Guernica was given not a Spanish code name, but was “Operation Rügen”. It was to provide the Luftwaffe with invaluable “practice” for the bombing techniques that were were to devastate Rotterdam and then Coventry in 1940.

On the afternoon of April 26, 1937, a market day, the first waves of the raiders, flying from bases in Burgos, struck the city from 4.30pm onwards. Wave after wave of Heinkel He111s, Dornier Do 17s and Junkers Ju52 Behelfsbomber — transports hastily, but effectively converted for bombing — flew over Guernica for the next two hours dropping their loads with impunity. A mixture of high explosives and incendiary bombs smashed buildings and set them ablaze, creating the conditions of “firestorm” that were to become familiar in the Second World War. As panic stricken citizens and their children tried to flee to the countryside they were strafed by Messerschmitt and Fiat fighters.

More than three-quarters of the city was destroyed. Contemporary photographs taken from the air show a desolate vista of jagged and charred stumps of what were once houses, civic buildings and churches. There was little enough of either industrial or symbolic significance in the city to aim at, but what little there was escaped damage, suggesting that terror not strategic gain was the raid’s object. A bridge, an arms factory and the ancestral oak were all unharmed.

While in Germany Goering rejoiced at this successful test of his young Luftwaffe, the rest of the world reacted with horror. When Steer got to Guernica in the small hours of next day he viewed the town: “a horrible sight, flaming from end to end . . . Throughout the night houses were falling until the streets became long heaps of impenetrable debris”. His report was published in The Times of April 28 and accompanied by a leading article deploring the “pitiless bombardment” by the Germans and sympathising with “the proud democrats of Vizcaya”. The Times was not, as a result, popular with a Nazi hierarchy long accustomed to an appeasing tone from the British establishment.

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