The Afro-American poet Langston Hughes visited Barcelona in 1937 as a newspaper correspondent for the Baltimore Afro-American. He saw the terrible destruction in the city caused by the bombing.
I came down from Paris by train. We reached Barcelona at night. The day before had been a terrific air raid in the city, killing about a hundred and wounding a great deal more. We read about it in the papers at the border. Last night, I thought. Well tonight, I’ll be there. Here (October 23, 1937)
He was inspired to write the poem Air raid: Barcelona (from here). The imagery is stark. East is back to Mallorca where Mussolini’s squadrons were based.
The death birds wheel East To their lairs again Leaving iron eggs In the streets of Spain.
Air raid: Barcelona by Langston Hughes
Black smoke of sound Curls against the midnight sky. Deeper than a whistle, Louder than a cry, Worse than a scream Tangled in the wail Of a nightmare dream, The siren Of the air raid sounds. Flames and bombs and Death in the ear! The siren announces Planes drawing near. Down from bedrooms Stumble women in gowns. Men, half-dressed, Carrying children rush down. Up in the sky-lanes Against the stars A flock of death birds Whose wings are steel bars Fill the sky with a low dull roar Of a plane, two planes, three planes, five planes, or more. The anti-aircraft guns bark into space. The searchlights make wounds On the night's dark face. The siren's wild cry Like a hollow scream Echoes out of hell in a nightmare dream. Then the BOMBS fall! All other noises are nothing at all When the first BOMBS fall. All other noises are suddenly still When the BOMBS fall. All other noises are deathly still As blood spatters the wall And the whirling sound Of the iron star of death Comes hurtling down. No other noises can be heard As a child's life goes up In the night like a bird. Swift pursuit planes Dart over the town, Steel bullets fly Slitting the starry silk Of the sky: A bomber's brought down In flames orange and blue, And the night's all red Like blood, too. The last BOMB falls. The death birds wheel East To their lairs again Leaving iron eggs In the streets of Spain. With wings like black cubes Against the far dawn, The stench of their passage Remains when they're gone. In what was a courtyard A child weeps alone. Men uncover bodies From ruins of stone.
The same site notes;
In the first two lines, he’s describing a sound (the sound of the air raid sirens) as if it’s a something visual (smoke). He probably does this for a number of reasons. It’s surprising, because we usually don’t think of comparing sounds and sights – it makes us stop to think, as it did you, to wonder why he would do that. Think about how smoke looks when it first appears – a little wispy, maybe a little transparent even. The siren sound is like that at first. Other sounds continue; maybe you have to stop and listen for a second to make sure that you’re really hearing it. Also, smoke acts as a warning that there’s a fire somewhere. Similarly, the air raid siren warns that enemy planes are approaching, about to drop bombs – which create fires.
As far as the number of planes – my guess is for one thing he didn’t want to simply march up the numbers because that would be sort of boring. But also, when enemy planes appeared, you might see one, then two, then five, then nine, then a whole bunch. You’d soon stop counting at all. The number of planes attacking are growing faster than the narrator can count, perhaps. That’s just an interpretation. It never occurred to me to wonder why he skipped “four” before. from here