G.K. Chesterton wrote that we are kept going in life by the notion of something around the corner. Almost as fascinating as this forward look is our propensity for looking back at history and asking, "What if?"

In this, his 13th book, Alfred Coppel tinkers with history by having lightning destroy the original A-bomb during its test at Trinity Site in New Mexico in mid-July 1945, an accident delaying the incineration of Hiroshima from August 1945 until the next March. The United States is forced to revert to the iron bomb and its earlier plan for the invasion of the Japanese homeland.

Most of the marines and soldiers training in the Pacific for Operation Olympic, the invasion of Kyushu, scheduled for Nov. 1, welcomed the A-bomb: operational plans estimated casualties running into the millions. Japan had never lost to a foreign power, the way of the samurai was to die, Shinto made surrender anathema, and the entire population--man, woman and child--fighting on its own turf promised the invading Americans the bloodiest confrontation in history.

Coppel's conception is remarkably well-researched. He has used the official assault plans and later military analyses of both sides, thus conferring credibility on his story, and his ability to blend the sweeping strategic and tactical detail of the antagonists is excellent. By winter 1945, eastern and southern Kyushu has been taken and many Japanese forces are retreating north to the Kanto Plain of Honshu for the final battle. Tojo has been returned to power by the militarists in Tokyo and is now a virtual shogun. The Americans decide to bypass northern Kyushu and launch Operation Coronet, the final assault on the Honshu heartland, on March 1. Coppel's plot concerns mainly this two-week period of land and sea battle before Hiroshima is destroyed in mid-March, bringing the war to a close.

As a panoramic sweep of men in action, the book succeeds. But on gritty detail and as a story believable in human terms, it falls far short of its brilliant conception. Like Clavell in "Shogun," Coppel is careless in his use of Japanese history and folkways (T. Yamamoto, author of the classic "Hagakure," was not a swordmaster, but only a samurai scribe who was never in combat; a soldier-wrestler was a sumotori, not a "sumitory"; Japanese did not refer to Americans as Yankees, nor did Americans call Japanese "slopes"--this epithet is two wars too early; and his contention that the thin wooden-shelled Shinyo suicide boats were safe from American radar overlooks the fact that they were propelled by metal engines).

Good writing would have overcome such stumbles. But when it occurs, it is fortuitous--one of several words Coppel should look up. On one page he has an American watching "for the smear of flame and smoke" marking the end of a Japanese spotter plane and 10 pages later he sees the twisting "smear of oily flame and smoke." In the acrid ambiance of close combat, soldiers always smell the last voiding of the bowels of the dying, and bladders flush from terror and elation--aspects of plumbing in battle properly untouched by Stephen Crane and later war analysts.

The main plot reunites Ranger Lt. Harry Seaver with his friends Kantaro and Katsuko Maeda in the neighborhood the three lived and played in as children. In an absurdly unreal denouement, Kantaro, now a colonel with the Imperial Forces, is wounded and slits his belly in seppuku, after which Seaver, his foe-friend, obligingly severs his head. Then, amid the din and dying, Seaver beds down with Katsuko, her energetic love-making doing much to belie intelligence reports that the Japanese were subsisting on less than 800 calories a day at the time.

All good war writing from "The Red Badge of Courage" (the Civil War) through Frederic Manning's "The Middle Parts of Fortune" (World War I) to John Horne Burns' "The Gallery" (World War II) tries, in Rilke's phrase, "to connect the terrible with the tender." Coppel fails to make the connection, and we are left with only a good idea gone glimmering.