Trained at the Slade alongside Mark Gertler, Stanley Spencer and others, Nevinson's career begins in restless technical experiment, a playing with painterly techniques from the recent past, a rapid shifting through styles successively reminiscent of Vlaminck, Picasso - of both the "blue" and the cubist periods - and others. Among the best of the very early works is an excellent exercise in English Impressionism, a school-of-Seurat painting of a railway bridge at Charenton dated 1911, with thick gouts of smoke wreathing a railway bridge. We cough and rub our eyes with cautious admiration.
By 1914, Nevinson was into Futurism, speed, mechanisation, modernity - he had become Marinetti's chief English spokesperson and ally. They even co-authored a manifesto called Vital English Art, which denounced Nevinson's hopeless homeland's various backward-looking mediocrities: "the pretty-pretty... the sickly revivals of medievalism, the Garden Cities with their curfews and artificial battlements, the Maypole Morris dances, Aestheticism, Oscar Wilde, the Pre-Raphaelites... the Post-Rossettis with long hair under the sombrero."
And so it was goodbye to Morris, whimsy and the Nineties, and hello to the excitements of war and modernity: "War is the only health-giver," proclaimed the benighted Futurists. And Nevinson went along with such idiocies until he got a taste of war's tangible realities while serving as an ambulance driver on the battlefields of France. Everything changed for him then - and so did the painting.
The images he made between 1914 and 1917 established his name as the most vital painter of the horrors of contemporary warfare. La Mitrailleuse (1915), for example, in which a group of machine-gunners huddle in a trench, scarcely more than dehumanised extensions of their weaponry, is a particularly fine example. Sickert called this painting "the most authoritative and concentrated utterance of the war". Other paintings of this period - First Searchlights in Charing Cross, for example, show how the new technologies of warfare seem happily suited to Modernist expressive techniques. But Nevinson steers something of a middle path between convention and experiment, now and later. In a work such as Returning to the Trenches, for example, the body of marching soldiers seem to move as one, locked together like some great machine in motion - which reminds one of Boccioni's experiments in the abstract depiction of speed - but they are also clearly, and fairly conventionally, recognisable, especially in the upper half of the canvas, as individual soldiers. Nevinson has adapted Futurism to his own needs.
Many of these canvases were exhibited at the Leicester Galleries in 1916. That show was an enormous success with critics and public alike, and a further exhibition, two years later, was equally successful. In part, this was thanks to Nevinson's spectacularly successful aptitude for self- publicity. In part, it was due to his images offering an honestly chilling alternative to official lies.
The best illustration of how Nevinson's approach to the Great War differed so markedly from that of his famous contemporaries is on show in a room that houses three great - in size, that is - paintings officially commissioned for the Hall of Remembrance from Stanley Spencer, Sargent and Nevinson. (Nevinson's is on a much larger scale than anything else he ever attempted.) Sargent's Gassed - which depicts a line of soldiers stoically trudging from left to right, many blindfolded, all heroic and upright in posture - is a quasi-propagandistic tribute to human dignity in the most undignified of circumstances, and it was praised to the skies when it was officially unveiled. Spencer's painting of a hospital interior is reminiscent of a church, with nurses flitting about, dispensing soothing balm to the needy, like a flight of angels. It is not so much a scene of war as the gentle, visionary apotheosis of one. Only Nevinson's The Harvest of Battle shows the disturbing and disgusting realities in their entirety - open- mouthed corpses; blundering soldiery; two armies suffering equally amid a welter of mud and squalor.
And then the war stopped, and Nevinson went on living for nigh on 30 years. In part, his predicament was somewhat akin to that of all those eastern European poets who drew so much emotional sustenance from opposing the Communist regimes that repressed them until, all of a sudden, in 1989, the regimes gave up the ghost and stopped the repression. And the poets were left with only their own navels to gaze at. What did Nevinson take for a theme in the aftermath of so emotionally all-consuming a subject as war?
Fortunately, at the turn of the 1920s, he found New York and its architecture, which amazed and delighted him for a time, and then, a little later, turned soulless on him. A number of fine lithographs came out of his renewed interest in urban landscapes. He rediscovered London, and some of his most expressive later works are haunting lithographs of docklands scenes.
But by the middle of the 1930s, the concentration seemed largely to have ebbed away, and his last works include several rather poor and mildly embarrassing allegorical paintings with such grandiose titles as The Twentieth Century (1932-35). In this painting a great, broody thinker, chin on hand, and straight out of Rodin, sits ponderously amid shambolically crowded, overlapping scenes. Soldiers are on the march, with bayonets flourishing skyward; red-flag-waving crowds are seething in the streets; skyscrapers soar vertiginously up and up in a skyscraperish sort of way; and planes buzz around in minatory, fly-like formations. Is this about the onset of Fascism? Vaguely, perhaps. But it's as much about a once remarkable talent now lacking, in its declining years, a focused theme to pit its wits against.
C R W Nevinson: Imperial War Museum, Lambeth Road, London SE1 (0171- 416 5000) to 30 Jan