Von Neumann’s War

“I can tell you what’s going to happen,” Cady said, kneeling to look through the sight. “They’re going to impact about halfway between us and the target, based on this aiming and the lay of the land.”

Alan smiled and pointed Shane to the monitor in a weapons van parked behind the firing pad. He thumbed the walkie-talkie that had been snapped to his belt.

“Range clear? Range clear?” Alan asked. When no one replied he keyed back in, “Range clear, we’re firing, firing, firing!”

Cady shrugged, then made himself cozy with the weapon. BBBBRRRRRRRR BBBBRRRRRRR! The weapon ripped out a series of bursts, all but one exactly five rounds. When he stopped he still had plenty of belt.

“Wheew!” Gries whistled. “Top, come look at this,” he added, shouting out the back door of the van.

Alan stood back for the two men to get a good view of the monitor displaying the target. The target was a half-meter square metal plate hung from a metal rack in front of a dirt backstop. The square metal plate was full of holes, all within the central third of the half-meter square. More than fifty holes were in the plate and all could be covered with a sheet of notebook paper. There was more hole than metal left in the center of the plate.

“You said that was three clicks?” Sergeant Cady asked in awe.

“That’s right,” Alan grinned like an opossum.

“How the hell?” Major Gries stepped back over to the weapon and began examining it closer. “It looks the same to me. What gives?”

“Well, sir, look at the belt. The rounds look funny. I didn’t want to say anything before; I figured it was part of the show,” Cady replied.

“They look like hollow-points or something,” Gries said.

“Close,” Alan answered. “They’re miniature jet engines.”

“Like Gyro-jets?” Cady asked. “Those things were inaccurate as hell.”

“No, not like Gyro-jets,” Alan said exasperatedly. “Hell, everybody always asks that!”

“What are Gyro-jets?” Gries asked. “And whatever they are, how the hell does this work? And why didn’t I know about it with what I was doing?”

“Here, look at this.” Alan reached in the van and pulled out a cut-away version of the round mounted on a board. “The round has an intake vent in the nose that forces the air through the vent down to the throat of the engine here, then the tail is a diverging rocket, er, jet nozzle. The flow of air is accelerated out the back, giving the round a maintained velocity of about Mach three point four. Since the round is spun, it’s therefore stabilized and the acceleration thrust vector cancels out lateral motion so it forces the round to stay on a straight-line path. There’s a crosswind effect, but even that’s muted.”

“Wait a minute. A jet engine? Where is the fuel?” Gries asked.

“Oh that. Roger or Tom could really explain it to you in detail, but it turns out that once the intake flow reaches speeds of Mach one or above the flow is continuously accelerated out the back without added energy,” Alan explained.

“That sounds like perpetual motion,” Cady said.

“Oh no, not at all. It really is just a phenomenon of supersonic flow dynamics. Scientists and engineers have known about this for at least three quarters of a century or longer. The velocity of a supersonic flow increases in a diverging nozzle.”

“Well, where do they get the initial energy from then?” Cady asked.

“You said it yourself, Sarge. The muzzle velocity is twenty-eight hundred feet per second. The powder in the round does that for us. Twenty-eight hundred feet per second is about Mach two point nine at sea level. So we see that the shell actually sped up before it got to the target.” Alan sounded giddy.

“Ain’t that some shit, sir?” Sergeant Cady added.

“How much range do these things have, Alan?” the major asked.

“Well, we don’t know. They’ve only been test fired here. We need to take them out to the desert somewhere and really test them. My guess is that sooner or later they’ll reach a speed or spin that the round can’t handle and they’ll just fly apart. But how far and how fast, I dunno.”

“Alan, this doesn’t feel like any kind of metal,” Cady said as he rubbed the tip of a round on the belt between his thumb and forefinger.

“That’s because it’s not metal. The nozzle design is too intricately detailed. There are side vents and stuff that I didn’t get into. And trust me, we don’t need to get into the CFD on this thing. But…”

“CFD?” Cady asked.

“Computational fluid dynamics. It’s a horrendous amount of math,” Alan said.

“Oh.”

“Yeah, oh. Anyway, the damned rounds are so complex that we have to build them one at a time in a laser rapid prototyping machine.”

“What the hell is a laser rapid prototyping machine?” Gries felt behind the curve. Alan was indeed knocking his socks off. He wished he’d spent more of his time working with stuff like this, rather than some of the silly shit he’d been chasing. Although Geckoman was still really cool.