As a teenage soldier in the trenches at Saint Éloi in 1915, my great-uncle Tim was shot through the chest by a sniper. The bullet passed straight through his body and killed the man standing behind him. He recovered in time to rejoin his unit in 1918 and take part in an attack on the German lines near Cambrai, during which he was shot through the right thigh, left leg and across the ribs.

“Since I wasn't dead, the only thing to do was crawl back up the hill,” he wrote. At the end of the war, Tim had a body full of holes and a Military Cross, but as he remarked ruefully: “I never actually saw a live German soldier.”

I was reminded of that sardonic wartime sense of humour this week by the publication of the diary of Captain Alexander Stewart, who recorded his life in the trenches with the same combination of grim wit and astonishing bravery. When shooting at “some blighter” about to fling a stick bomb at him, he finds the smoke from his pipe getting in his eyes and obscuring his aim. “Much to my annoyance, I had to put my pipe in my pocket alight... it was lucky it did not burn my jacket.” Captain Stewart jokes about the rats that lick the brilliantine off his hair, the idiotic commands from generals who should be “taken up to the line and frozen in the mud” and being injured in the throat by a piece of shrapnel, which he coughs out and then picks up as a souvenir.

We are all familiar with the First World War of blood and mud, of lions led by donkeys, the futility, the boredom and the slaughter. Less well remembered, however, is the pitch-black humour of the trenches, the jokes and wry amusement of men laughing in the face of death. The war was never remotely fun, but it was occasionally funny, or made to be so.

Every year we remember the pity of war, but very seldom the peculiar wit of that dreadful war, which was one of its most extraordinary legacies.

Jokes were a vital defence, a way for soldiers to deal with the vile ludicrousness of the man-made hell they were in. As Wilfred Owen wrote: “Merry it was to laugh there/ Where death becomes absurd and life absurder.” The First World War left an entire generation scarred, physically and psychology, but it also bequeathed a shared sense of the grotesque, a collective desire to shrug off horror with a joke, to make light of death.

This aspect of the national character re-emerged strongly in the Second World War, when humorous propaganda was dropped over France, Lord Haw-Haw was belittled by mockery, the Ministry of War employed an official cartoonist and almost every wartime movie had a role for the chirpy cockney jokester, bantering away as the bombs and bullets fly.

British martial humour remains an odd but enduring weapon of war. In 1982, after HMS Sheffield was struck by an Exocet missile, her crew sang Always Look on the Bright Side of Life from Monty Python's Life of Brian as the vessel sank. Even today, bogged down in Helmand or Iraq, the British squaddie struggles to raise a laugh whenever a cameraman or reporter approaches: in some unstated way it is part of the uniform.

Officers in the Great War often expressed astonishment at the unshakeable, cynical and usually ribald sense of humour in the ranks. Sidney Rogerson, a survivor of the Somme, described how the average soldier, “when by every law of nature he should have been utterly weary and fed up, invariably managed to be almost truculently cheerful”. Little of First World War humour has stood the test of time (humour seldom does). Jokes about trench foot, army rations and blimpish long-forgotten majors no longer amuse; the drawings of Bruce Bairnsfather, foremost of the Great War cartoonists and a vital source of humour for men in the trenches, are now more likely to make us cry than laugh.

The Wipers Times, printed on a press salvaged at Ypres, was the Private Eye of the Western Front, offering lampoons, satire, jokes, reflections and poems: “There was a young girl from the Somme/ Who sat on a Number Five bomb...” Its authors, ordinary soldiers, mocked the senior officers, the self-inflating war correspondents and themselves. They even parodied the letters page of The Times: “Dear Sir,” wrote a reader, not long after the barrage of the Somme began with a noise so loud it could be heard in Sussex. “As I was going over the top last week I distinctly heard the call of the cuckoo. I claim to be the first to have heard it this spring and should like to know if any of your readers can assert they have heard it before me?”

As military psychologists know, humour is far more effective at binding men together than coercion or fear; laughter reduces tension in combat, offering a small affirmation of life amid the fear and bloodshed. Irony and jokes, the darker and ruder the better, offered Great War soldiers a way to reclaim individuality, when life and death was in someone else's hands. “Each joke is a small revolution,” wrote Orwell. Nowhere is this truer than on the battlefield.

In an instinctive way soldiers facing muddy death reached for humour as a lifeline, almost literally, and sometimes heartbreakingly. Corporal E.C.East, of the 2nd London Regiment, was injured in the face by shell splinters during the attack on Aubigny au Bac. Looking for an orderly to dress the wound, he came across a young soldier of his platoon, mortally wounded. As East leaned over to give him a drink, the wounded man looked up at East's blood-streaked face and remarked: “Crikey, your barber was ruddy clumsy this morning.” A few moments later, he was dead.

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