It was clearer on the paper plot, and Cavanaugh immediately understood their dilemma. The gap in the minefield was covered not by one acoustic sensor, but two, one to either side.
“It makes sense that the mines and sensors wouldn’t line up,” Weiss remarked. “They have different detection ranges, after all.”
Now we have to muffle two sensors,” Ford muttered. “The Russians are not playing fair.”
“They don’t even know we’re playing,” Jerry reminded him.
They’d added in circles that represented the detection range of the acoustic sensor on the geoplot, along with the diamonds that marked their actual positions on the sea bottom, and the two mines on either side of what everyone now called the “The Toledo gap.” Cavanaugh was visualizing them as goal posts.
The two acoustic detection circles overlapped in the gap, a little to the left of center. Weiss asked, “What if we use the UUVs to mask this one on the right?”
Ford tapped a few keys, and measured the distance. “Four hundred yards,” he reported. “Maybe four twenty-five.”
“Compared to a thousand before,” Jerry observed. “I’m sure we could get through that, carefully, on the way in. It’s the way out I’m worried about. We can’t expect to have the UUVs navigating for us.”
“And we might be in a hurry,” Weiss added, smiling.
Jerry asked, “How long to ‘bomb’ one sensor, come back to the sub, reload ballast, and then do it again?”
“Assuming we can do it at all?” Weiss asked. “Too long. I feel like the clock is ticking.”
Other heads nodded, and Jerry suggested, “Then let’s see first how well the UUVs can imitate a glider.”
With both UUVs back aboard, Carter proceeded five miles northwest for “flight tests.” To Cavanaugh, it seemed they should have moved farther away from Russian territory, but Captain Weiss reassured him. “We can’t hear the Russians this far away, and I guarantee we have a much better sonar suite than they do.”
While Jerry and the UUV team tested Walter, Captain Weiss had the sonar crew keep a close watch. Although she wasn’t particularly vulnerable with a UUV deployed, it would be highly inconvenient if a Russian stumbled across Carter while they were occupied experimenting with the remotes.
They launched José with as much ballast as the UUV could hold, almost a hundred pounds of lead shot. The UUVs normally carried some ballast to maintain neutral buoyancy, but the UCC crew had filled the ballast compartment, so the UUV was “max heavy” when it left the sub.
Lieutenant Ford, worried about the extra weight, watched the battery charge and speed carefully as LTJG Lawson moved the UUV a few hundred yards off Carter’s port beam. While Carter hovered above the bottom, José rose, or more accurately, “clawed for altitude” like a heavily loaded airplane. The UUV needed full power and a nose-up angle to slowly rise. It took longer than normal for the vehicle to reach a depth of twenty-five feet below the ocean surface, but once leveled out, it proved to be only two knots slower than its normal eight-knot maximum speed. It still needed a little up angle, and of course maximum power.
After taking copious notes during the UUV’s ascent, LT Ford reported, “I’ve got the numbers I need, Commodore. Ready for the first test.”
Cavanaugh watched Mitchell glance at the recorded values, and at the display, before reporting on the intercom to control. “Ready for glide test.”
Weiss immediately replied, “Proceed.” The displays in control would let them see everything that they saw in UCC.
Jerry nodded, and told Lawson, “All stop, five degrees down angle.”
The bottom lay some three hundred feet below José. They’d calculated the sink rate using the standard formulas in the UUV manual. That much was easy. What they couldn’t calculate was how far forward José would move as it descended. The UUV had no wings, just small control fins at the back.
Everyone’s attention was focused on the readouts: battery charge, depth, and especially speed. Even though everyone could see the displays, Lawson still read them out loud. “Showing six knots.” Normally, at that speed, the vehicle would coast to a stop within a minute of the motors stopping. It had a smooth exterior, but nobody who saw one would describe it as “streamlined.”
“Still showing six knots,” Lawson reported hopefully. Up in control, they were plotting the UUV’s position, as well as its depth. They needed to know exactly how long the “bomb run” would have to be.
Cavanaugh watched the display along with everyone else. It actually showed the UUV’s speed to a tenth of a knot. When Lawson had nosed over, it read 6.2 knots. Then it went up, to 6.4.
After another moment, the lieutenant announced, “Speed is up to seven knots,” a little surprised.
“Sink rate matches what we expected, more or less,” Ford commented.
Cavanaugh watched the speed go up again, to 7.5 knots. Well, most things go downhill faster than they do over level ground.
“Eight knots!” Ford announced proudly, as if José were in a race. “Sink rate is increasing as well.”
“End the test,” Jerry ordered suddenly. “Engage the propulsion motor and bring it level. Be ready to bring the nose up. Steve, watch the sink rate and depth carefully.”
Puzzled, Ford gazed at the commodore, who looked genuinely concerned. The vehicle had only gone down about a hundred feet, and Cavanaugh knew the plan had been to let the UUV drop until it was much closer to the bottom, and maybe even find a feature on the seabed to practice their aim.
Jerry repeated, “Watch the depth carefully. Be ready to angle up if I say so,” he ordered. Lawson acknowledged the order, but both he and Ford looked confused. Jerry explained to the two lieutenants, while keeping his eyes on the display, “We’ve determined that the UUV will gain sufficient speed as it sinks, in fact, a little better than expected. But it’s translating some of that speed into downward motion. We know it will dive like an airplane. The question is, can it pull out of a dive like one?”
Cavanaugh imagined one of their priceless UUVs plowing into the bottom at ten-plus knots.
“Speed’s not dropping a whole lot. Sink rate is slowing…”
“Raise the nose ten degrees,” Jerry ordered.
Ford, making notes, announced, “That’s the trick! Look at the speed drop. And the descent rate is decreasing.” After a long pause, he reported, “Sink rate is zero.”
“That’s called a ‘flare,’” Mitchell explained. “Pull the nose up just a little, and the bottom of the plane — the vehicle — turns into one giant speed brake. The trick is going to be flaring close enough to the bottom to kill the sink rate, but leaving the UUVs at the right depth to drop the lead shot on the sensor.”
“A steeper up angle — a flare — would do that quicker,” Ford suggested hopefully.
“But we don’t want the UUV to rise,” Mitchell cautioned. “We want to slow the vehicle down just a bit as we’re approaching the sensor node. In aviation, they call that ‘dumping speed.’ But the borderline between losing a little speed and losing a lot is very fine.”
“We need to do some more tests,” Ford realized. “Maybe a lot more.”
Jerry reached for the intercom. “I’ll inform Control. You figure out exactly how much longer this is going to take, and then how to do it faster.”
“Some more time will be required.” Jerry passed on to control what had happened. He could hear the frustration in Weiss’s voice over the intercom. “But I concur. It has to be done. Besides, my sonar gang just came up with a way to solve the problem of the buoys not lining up with the Toledo gap.”