Sledgehammer Three was a rugged sphere almost four hundred kilometers in diameter. As far back as the twentieth century, it had been recognized that above a certain minimum mass an astronomical body's own gravity would prevent it from retaining a grossly irregular shape. Only four of Sol's asteroids were above that minimum. Here in Home Hive Two's fifth orbital position, though, it was pretty clear that the unborn planet would have been a true whopper if it had succeeded in clumping together. In spite of a vastly greater radius, this asteroid belt was as dense as Sol's, and held far more giant members. The three Sledgehammers had been easy to find, the six smaller rocks for the mere Hammers effortless.

Then had come the toil of constructing the installations which Taliaferro now observed. Over a hundred robotic point-defense emplacements dotted Sledgehammer Three's wild and barren surface. Also, buried deep under the crevasses and craters, were the command datalink facilities that would enable Taliaferro's eleven Guerriere-C-class command ships to coordinate the three Sledgehammers' defensive fire. The six Hammers mounted proportionately lighter defensive works.

All of that, however, was secondary, meant only to keep these asteroids in existence long enough to fulfill their destiny. Only one engineering work on Sledgehammer Three really mattered-the one that couldn't be given a trial run.

"Get me Commander Lin," Taliaferro muttered. The pilot had barely complied before he leaned forward and snapped into the grille. "What's the word on that flaw in the pusher plate?"

"We're not certain there is one, Sir," Lin Yu-hsiang replied from his temporary command post on the surface of Sledgehammer Three. "When it comes to constructing Orion drives, we don't exactly have much experience-and having to stop what we're doing to answer questions about it doesn't exactly help!"

The pilot blanched, expecting thunderbolts. But Taliaferro actually chuckled-partly in recognition of a kindred spirit, and partly at what had become a standing joke in TG 64.1. When the name for what the task group was constructing had reached the Tabbies, they'd thought they were being honored. No one had had the heart to tell them that the name dated back to a time centuries before humanity had dreamed their race existed.

Nuclear pulse propulsion-"Project Orion"-had been a product of the twentieth century, one of many notions for liberating the infant Space Age from the dismal mathematics of chemical rocketry. Conceptually, it set some kind of record for brute-force crudity: detonate a series of nuclear explosions behind you and let them kick you forward! Naturally, it required a massive shock-absorbing plate for your vehicle's rear end. Worse, however, it had faced insurmountable political obstacles in a world understandably jittery about allowing anyone to send up spaceships packed full of what were in effect hundreds of small nuclear weapons. But for a time it had seemed to offer the best hope for reaching the outer planets and-especially after the Bussard ramscoop had come to grief on the hard facts about the interstellar medium in Sol's vicinity-the stars.

Then had come the unanticipated breakthrough into reactionless drives, and the Orion concept had gone the way of Jules Verne's giant cannon. At the same time, the idea of "dinosaur killers"-asteroids used as kinetic-energy weapons against planets-had joined reaction drives in the dustbin. It just wasn't practical to enclose an entire asteroid in a drive field. And tractoring such an object would have no effect except to rip the tractor-beam projectors out of ships that instantaneously took on velocities measured in percentages of c.

No, it couldn't be done with reactionless drives . . . but Vanessa Murakuma had wanted it done anyway. When she'd put the problem to Taliaferro, he'd automatically snorted that it was preposterous. Then he'd gone off and thought about it, to the near-exclusion of eating and sleeping. And when he'd put his solution before her, she'd backed him to the hilt, selling the idea to a skeptical Joint Chiefs of Staff.

Taliaferro's moment of amusement passed.

"I tell you what, Commander," he said. "You've got precisely as long to decide whether there's a problem-and, if there is, to fix it-as there is between now and Sledgehammer Three's scheduled ignition."

"But . . but, Commodore-"

"But me no buts, Commander. I've just finished checking out all the other asteroids, and they all report that they're ready for ignition. The first of them, Hammer Four, is due to light off in-" Taliaferro glanced at his wrist chrono "-thirteen minutes and a little less than twenty seconds. After that, there's no turning back. I'm damned if I'll stop the clock now to wait for you to get your act together!"

"Commodore, I protest!"

"Protest all you want to, Yu-hsiang-later. But right now, if I were you I'd get busy on that pusher plate. Sledgehammer Three is going to get kicked out of its orbit on schedule, and if you're still there at the time . . . well, it ought to be an interesting trip to Planet III, especially with fusion bombs going off under your ass!"

Taliaferro cut the connection while Lin was in mid-splutter, and turned to the pilot.

"All right, get us back to Alfred. And raise Fleet flag."

While he waited, Taliaferro studied a two-dimensional schematic of the Home Hive Two A System out to and including the asteroid belt. Sheer habit, for he'd long since memorized it. Still, he gazed at the little lights of the nine asteroids which TF 64.1 had transformed into weapons. They were strung out over forty-odd degrees of the belt's circumference, a curving scimitar of death. That was where they'd been found, and it had been out of the question to move them together, for the same reason their drives couldn't be tested: an Orion drive in operation was something the Bugs could hardly fail to notice. So they would start moving in staggered order starting with Hammer Four, each asteroid lighting off its drive as the others came up level with it on the hyperbolic orbit that would send them careening across the inner system, terminating at one of the three scarlet planet-icons on the display. Sledgehammer Three, the tip of the scimitar, would be last, so Lin actually had a fair amount of time left. Just as well, Taliaferro thought. I wouldn't really leave him there. Probably.

He'd barely finished reporting to Murakuma across the light-minutes when a multi-megatonne fusion fireball awoke a few score meters behind Hammer Four, its brilliantly defined shock wave surging toward the asteroid but never quite touching it. Then another . . . and another . . . and slowly, ponderously, Hammer Four began to move out of its immemorial orbit, trailing what looked (or would have looked, to anyone who'd braved the sleet of gamma rays) like a trail of small suns connected by a stream of glowing gas.

Operation Cushion Shot had begun.

It had taken an appreciable amount of time for the realization of what was happening to sink home through layers of unexpectedness-not a fatal delay, perhaps, but certainly a disadvantageous one. But there was no longer any room for doubt. The orbits into which those asteroids had been moved could be projected without difficulty, and all of them intersected at the point that would then be occupied by the third planet. Calculating the kinetic energy such impacts would release was equally simple. And the Fleet knew only too well what would happen to the system's remaining defenders at the instant that planet's population died.

Abandoning the outer system to the Enemy had been an error. That it was an error grounded in flawless logic was no excuse. Neither was the totally unprecedented nature of what the Enemy was doing.