Escape to Nowhere, Steven Spielberg's first film, was shot on 8mm in 1960, when he was twelve years old. It was a Second World War action adventure; not surprisingly, for Spielberg grew up with the Hollywood war film—with, to be precise, two kinds of war film. The early ones, like William Wellman's Battleground and Henry King's 12 O'Clock High, drew on first-hand experience to explore soldierly brotherhood, group dynamics under pressure, and the strains of command, with some lingering tang of authenticity. But by the later 1950s the genre was changing. The Hollywood war movie simply became a springboard for action adventures, and the Second World War had to compete with spies and gangsters until, eventually, it was eclipsed by Vietnam. By the late 1970s, the Second World War had ceased to be of interest to popular film-makers.

Why then has Spielberg now returned to it? Partly because his childhood passion still burns; partly because the Second World War has come back into literary fashion, as a generation which fought as very young men, now tells its tale. (Many of the books discussed in Samuel Hynes's recent The Soldier's Tale were not around in 1989, when Paul Fussell published his Wartime.)

War memoirs famously change tone with the passing of time—Edmund Blunden's first version of Undertones of War was more cheerful than the one he eventually published. Today's memoirs are inevitably affected by Vietnam and the cynicism about all wars and institutions it fostered; coloured, too, by an emphasis on the traumatic impact of war which was still unknown in 1945, when it was assumed that a normal person, properly trained and led, could come though anything.

Vietnam has also spawned a new kind of military history. The enormous success of “oral histories” of that conflict not only transformed the image of the Vietnam veteran (from baby-killer to victim); it gave the testimony of the individual soldier a new legitimacy and authority, sweeping aside traditional reservations about his limited perspective and imperfect recall. In this new climate, the memories of Second World War soldiers—especially of front-line infantrymen—take on an almost priestly authority.

Part of Spielberg's intention in Saving Private Ryan is to honour these memories. His film opens and closes with clumsy “bookending” sequences—in which an aged veteran, accompanied by his family, visits the Normandy cemeteries; and it takes its plot from a recent work of oral history, Stephen Ambrose's Band of Brothers (1992). But interwoven with this are elements of those Hollywood war films he grew up on. Which is why Saving Private Ryan, at 170 minutes long, is, in effect, three different films—sitting uneasily within the contemporary “framing”. The first, running at twenty-five minutes, re-creates the landing on Omaha Beach on June 6, 1944, much as remembered by veterans—bloody, terrifying and pointless. The second, ninety minutes long, follows a group of Omaha survivors, led by Tom Hanks, who are sent to find Private Ryan, a paratrooper whose three brothers have all been killed; the War Department wants him “saved”. This is Spielberg revisiting the world of the post-war buddy films, of GI Joe and A Walk in the Sun. The third is devoted to the immense battle which ensues when Hanks and his men, having found Private Ryan, join him and his unit in defending a bridge against German attack—the war adventure film of the 1960s, staged with 1990s special effects.

From the moment the bow doors of a landing craft open and a tempest of machine-gun fire devours the leading group of men, the Omaha Beach sequence is overwhelming in its power and horror. The sheer violence of modern warfare, the ballistic force with which steel destroys flesh, the confusion of battle, the shock of wounds, have never been better conveyed. The use of hand-held camera and bleached-out colour are masterly. As Hanks's group of Rangers struggle up the beach and somehow devise a way of outflanking the German bunkers, the audience, heart in mouth, rides out the storm, suspending judgment until a measure of calm returns.

It proves, though, a hard act to follow. Having dispensed with the usual pre-combat character build-up (chaplains giving confession, GIs writing home, crap games, and so on), Spielberg now has the double task of establishing character and unfolding narrative—half an hour into the picture. These have never been his strengths, and the job is badly botched here, with a sequence in the Pentagon veering uncertainly between satire and veneration and Mrs Ryan, mother of the three dead brothers, depicted sitting on the steps of a Saturday Evening Post Norman Rockwell house.

The whole of the lengthy second section, in which Hanks and his men go looking for Private Ryan on the Normandy battlefield, finds Spielberg struggling for coherence. A series of engagements and encounters—with German snipers, French civilians, American paratroopers—are all staged with relentless overemphasis, and the portrayal of the rapport between men in groups which comes easily to Howard Hawks and Anthony Mann is notably absent. Each scene makes a trite point at great length—being nice to children will get you killed, killing prisoners is inevitable in war. The minutes tick by, endless badly written monologues are delivered, and one longs for Mann's skill in filleting a scene, his understanding of pace. But the problem lies much deeper than that: the fundamental dramatic premiss of the film that “saving Private Ryan” will somehow redeem the horror of it all—that, to quote Spielberg, “the nobility of that mission becomes a symbol. His going home represents them all going home”—is hollow. It cheapens everything that has gone before.

Historically, Spielberg has a point. The Americans never saw the war as the British did; have never quite shared the view that “for those who took part in it, the Second World War had a great deal of point”. Talking to soldiers in 1943, Arthur Miller looked in vain for “some ideological conception animating them: the war was ‘about’ little more than what a game of football is ‘about’—something that had to be won for pride's sake”. Karl Menninger, the American Army's chief psychiatrist, found that whereas the Russians were fighting to avenge their loved ones, the British for survival, and the French to get back their country, “the doughboy fights because he has to. He fights for his buddies and because his self-respect won't let him quit!” Like their Civil War forebears, GIs suffered terribly from “nostalgia”—a passionate wish to get home—which worried their generals. It may also be that the post-war films played this down and gave the American soldier a sense of collective purpose he did not feel at the time. None of that can alter the fact that, dramatically, Spielberg has made a huge error of judgment.

The film improves when Hanks finds Private Ryan. The director relaxes at last—there is a good scene of tired soldiers listening to a Piaf record. Matt Damon, playing Ryan, has a humanity which transcends banal dialogue. The last half-hour brings a tangible sense of relief. Back with war as action adventure, Spielberg can forget character and concentrate on machinery, “the film director as junior mechanic” as David Thomson once called him. His command is reimposed. The final battle is, of its kind, brilliant; dominated by an extraordinary soundtrack, by the voices of weapons not actors. Each brand of machine gun has its characteristic noise, each German tank, roaring, whirring and grinding, shakes the cinema to its foundations; but the scene-stealer is a German flak-gun, manhandled into action and pumping out cannon shells with lethal insistence. But this extended mechanical ballet further devalues the Omaha sequence at the head of the film. It is pure invention; no such battle ever took place.

Some have compared the realism of Saving Private Ryan with the distortions of Hollywood's last visit to the D-Day beaches, Darryl F. Zanuck's The Longest Day. It is true that Zanuck—who believed that “there is nothing duller on the screen than being accurate but not dramatic”—took terrible liberties with events on Omaha Beach; tended to reduce each battle to a star cameo and was over-kind to German generals. But The Longest Day contains sequences as memorable, if not as gory, as Spielberg's Omaha and had a sense of perspective. Having lived in Europe and dallied with chanteuses, Zanuck understood the overall significance of D-Day. His film made clear the central historical truth that the men who died at Omaha did not die in vain; they helped to liberate Europe. Zanuck would certainly have cut a good half-hour out of Saving Private Ryan.

But that was in another era. Perhaps it is mistake to expect artistic unity from the modern blockbuster. Maybe Saving Private Ryan is better compared to the naval bombardment before D-Day, systematically locating and subduing its different target audiences in turn. It seems to be making big money and may herald a revival of the war film. It will be interesting to see what Terrence Malick, a more gifted filmmaker than Spielberg but an equally incoherent storyteller, makes of James Jones's Thin Red Line.