IMAGINE, if you will, that in the spring of 1942 Japanese air and naval forces are moving inexorably southward toward Australia when they encounter an American fleet at the Coral Sea. You know what happens: In the decisive Pacific naval battle of World War II, the Japanese are turned back and their continued expansion is thwarted. But no. This is how John Hooker imagines it: "In May, the American naval forces attempted to halt the Japanese drive south at the Battle of the Coral Sea; but after a three-day engagement, in which they lost four capital ships and dozens of smaller craft, they were forced to retire." Onward the Japanese forces move: "The invasion of Australia began on 12 June 1942, with Japanese landings at Darwin, Cooktown and Cairns. . . . The eents of the outside world had come to Australia."

Thus we have the shocking central premise of The Bush Soldiers, an exceedingly powerful, gripping, intelligent novel. Not merely does it postulate the invasion of Australia, but it sees that country as reeling helplessly under the Japanese assault. Given only token help by the British and deserted by MacArthur, who has fled to New Zealand, Australia soon finds the major cities of its southeast coast occupied by the Japanese, who press steadily westward opposed only by the remnants of the Volunteer Defense Corps, whose orders are to "go into the bush and fight," to "harass, deny and destroy."

One member of that corps is Geoffrey Sawtell, a veteran of World War I who is now in his early forties. He hates war but loves soldiering, and after a hiatus of two decades he now finds himself once again doing both: "So, he thought, it is ten past eleven on a spring day in the Year of Our Lord, 1943. I am riding with my mate Frank Counihan, I have lost my wife, but I have valuable possessions and skills and I shall join the Englishman, Major St John Jackson, to see what shall be done. Like Counihan ahead, he started to sing:

"We'll wander over mountains and we'll gallop over plains -- For we scorn to live in slavery, bound down by iron chains."

Soon there are five of them: Sawtell, Counihan, Jackson, a British padre named Sergius Donaldson and Kevin O'Donohue, a young Australian. They have little in common except: "We are all soldiers and we have a common enemy." They have no specific orders, so Sawtell chooses a mission for them: "To sabotage the Zinc Corporation Mine at Broken Hill. It's a prime military target." Thus they set out, on horseback, across the outback on what is for Donaldson, and indeed for all of them, "a chance for retrieving honor, for courage and for striking back at evil and bestiality." It is a trip of several hundred miles through a "dull and menacing land," occupied now only by the Aborigines and by a ghostly enemy whom they imagine and fear more often than they see and encounter. Beyond that it is an essentially quixotic mission, inasmuch as the sabotaging of the Zinc Corporation Mine cannot have any significant effect on the Japanese occupation; yet in the same spirit that moves the Resistance in France, half a world away, they press on.

NOT MERELY is it a journey toward a military target; gradually it becomes a journey through Australia itself, which Sawtell fancies to be "the best place in the world" but Donaldson can see only as a wasteland: "Are there any cities? I haven't seen them. Are there any cathedrals? I haven't seen them. I sometimes think God has forsaken this place, it's like no other country I've ever known." As a civilian, an engineer working for the Country Roads Board, Sawtell had seen himself as "helping to build Australia." Now, as a soldier, he is not merely helping to defend it against the Japanese invaders, but attempting to uphold its dignity and history against the contempt and misunderstanding of the English -- the same English in whose cause he and thousands of other Australians had fought in Belgium and France two decades earlier.

That war is the shaping experience in Sawtell's life. Serving for a year in the front lines, he had survived the hell that killed thousands of others, many of them his friends, and came out of it with a sense of having been "cast out" from normal society: "He had been to a place where they would never go." Years after the war, when a memorial is being dedicated and his wife protests against it, Sawtell explodes:

"I've seen men holding their guts in their hands, I've seen men coughing their lungs out with mustard gas, I've seen strong men crying, I've seen men mutilated: legs, arms, noses, private parts; they're still hidden away now in repatriation hospitals. Don't tell me I like war. What you and your friends fail to understand is that the Shrine is all we survivors have got, it holds us all together, we've been where you lot haven't, you've got no bloody idea, and all you can do is try to bugger it up. You don't hand a soldier an anti-war pamphlet; you respect him, or at least, leave him alone."

It is this same sense of soldierly obligation that drives Sawtell and his four cohorts onward, through a journey that Hooker describes with such biting detail that the reader is drawn wholly into it: the heat and the dust, the polluted water tanks, the frightened but hostile Aborigines, the desperate foraging for food and liquor in roadside hamlets that have already been pillaged into unrecognizable rubble. The Bush Soldiers is not so much a war story -- there is actually no significant encounter with the enemy in it -- as one of men who are determined to accomplish their mission. In its depiction of the bonding of unlikely allies it recalls Seven Samurai; Hooker's warriors, like Kurosawa's, are united not by personality or education or background but by their common commitment to a soldier's honor.

Yet they all yearn for peace: "They stopped at a garage and found the remains of a Hupmobile. Sawtell looked at the big American car and thought of the years after the war, of picnics, of Marcia and playing tennis on country grass courts." The sense that permeates the novel is of deep, irrecoverable loss; the passages in which peacetime is recalled positively ache with longing and regret, with a desperate desire to rip away the terrible present and somehow to be happy again. But for Sawtell and his warriors that is not to happen. They accomplish their mission and move on, deeper and deeper into the unknown Australia, farther and farther away from any hope of rest. It may seem a sad, cruel way to end this splendid novel, but Hooker is an honest writer and he knows he has no other choice.