If you read JBS Haldane’s entry in Wikipedia and you should, you will not read about the Spanish civil war.
You can read about it in Virginia Cowles’ Looking for Trouble.
” A few days after I arrived in Madrid I met Professor J. B. S. Haldane, an English scientist and former don at Cambridge University, who was lunching at the Gran Via restaurant. ‘Think I’ll hop down to the battlefield and have a look round,’ he said casually. ‘Do you want to come?’
An hour later I found myself walking along a street on the outskirts of the city. The Professor cut an eccentric figure in a pair of breeches too tight for him and a tin hat with a broken chin-strap, left over from the Great War, which he’d brought from England. As it was the only tin hat in the whole of Republican Spain, it attracted a good deal of attention from passers-by, and twice sentries saluted us respectfully, obviously impressed. Although Haldane had come to Spain to advise the Government on antidotes for gas, he liked to pass himself off as a joke character. When anyone asked what he was doing in Madrid, he always replied, ‘Just a spectator from England. Enjoyed the last war so much I thought I’d come to Spain for a holiday’.
… It was ghostly and sad with the wind whistling through the window frames, and doors high above banging back and forth on empty caverns, but the Professor’s spirits were high. He was just remarking on how fine the weather was when there was a loud whistle. A shell hit the brick house on the corner and another plunged into the pavement. We stumbled into a doorway and stood against a dark wall while several more passed overhead. After a few minutes the Professor decided it was safe to continue. ‘Anyway’, he added, with all the disdain of the World War veteran, ‘they are only little shells, so come along’.
My confidence in the Professor was shaky. I thought he was making too light of the situation, and the prospect of the front was growing more alarming every minute. However, at this stage there seemed little else to do but follow. “ (Looking for Trouble, Virginia Cowles)