Captain Mealey had never fired a torpedo at an enemy ship and he wanted to know why Joe Grenfell and Dusty Dornin had missed. Joe Sirocco, a trained mechanical engineer with a retentive mind, had been aboard Gudgeon during the pre-war torpedo firing record and during Gudgeon’s first two war patrols. Sirocco tried to explain why the difficulties in hitting an enemy ship existed in terms that wouldn’t offend Captain Mealey’s stiff-necked Academy pride, why the Navy’s peacetime training for submarine torpedo firing had been so wastefully inefficient.
The difficulty, as Sirocco saw it, was rather simple. Basically, seven factors had to be determined to work out the mathematical formula necessary to hit a target ship with a torpedo. The firing ship’s course and speed were known, as was the speed the torpedo would travel. The course of the target ship, its distance from the submarine at the moment of firing, and at the moment the torpedo arrived, and the distance the torpedo would have to run were not known and had to be determined.
The distance of the target ship is not difficult to determine if sufficient time for periscope observation is available. An instrument in the periscope called a stadimeter gives that distance if the height of the target ship’s masts is known. The course of the target ship can be determined by the “angle on the bow (or stern)” that the target ship presents to the officer manning the periscope. The angle on the bow or stern is purely a judgment factor made by the periscope officer. If the target changes its course, if it zigzags or if it varies its speed from time to time then these factors must also be considered and worked into the torpedo problem.
The difficulty, as Sirocco saw it, was that the Navy had used its own destroyers for submarine targets. The submarines fired torpedoes equipped with “exercise” warheads, dummy warheads that were filled with water that was blown out of the head when the torpedo run was completed so the torpedo would float, head upward. A smoke pot in the exercise head aided in the recovery of the torpedo.
Submarine officers knew the height of the destroyer masts to the inch so estimating range was simple. They knew the outline of the destroyers so well that estimating the target ship’s course by its angle on the bow or stern was routine.
There was no information on the height of Japanese masts on merchant vessels. Japanese warships periodically lowered or raised the overall height of their masts to confuse a submarine captain. The unfamiliar silhouettes of Japanese ships, the often oddly shaped bow and stern lines of those ships were also confusing and often made the determination of the vital angle on the bow or stern a matter of wild guesswork.
To further complicate the difficulty it was widely believed that in firing an “angle shot,” a shot in which the torpedo is fired out of the torpedo tube and then changes course, by means of a pre-set gyroscope within the torpedo, that if the torpedo was fired in the direction of the Earth’s spin, i.e., to the west from a ship facing roughly north or south, the torpedo would skid farther in making its turn than if it were fired in the opposite direction.
“As I see it, sir,” Sirocco summed up his arguments the afternoon before the Japanese battleship was due to arrive at Truk. “As I see it, making an approach on a friendly destroyer in peacetime and doing the same thing out here on an unfamiliar target is two different kettles of fish.”
“Granted,” Mealey said. “If Joe Grenfell and Dusty Dornin had trouble then all of us who aren’t as good as that pair at firing torpedoes are going to have a great deal of trouble. The way it looks to me is if the target is valuable enough you go in to point-blank range, eight hundred yards or less! Preferably from a place abeam of the target so we don’t get confused by the angle on the bow of a type of ship we’ve never seen before.” He reached for his coffee cup and took a swallow.
“According to the intelligence report the battleship and its escorts should show up before dawn tomorrow, just before dawn. We should be able to get a fix on them with the periscope before we dive and then we can track them on sonar. We’ll go deep, two hundred and fifty feet and hug the reef. There’s a shelf there on the chart that shows about four hundred feet of water and then it drops off to over a thousand fathoms. If we stay on top of the shelf until we’re ready to commit ourselves they shouldn’t be able to pick us up on sonar.
“When we’ve got the problem down pat with sonar bearings we’ll come up, confirm the problem factors and start shooting!”
Sirocco rubbed his craggy face with a big hand. “Armor plating,” he said. “That battleship is armor plated way below its water line. Our exploders are modified for contact hits. You’ll have to set them to run deep, hit her below the plating.”
“Armor plating usually goes down twenty feet below the water line,” Mealey said. “I’ll set the torpedoes for twenty-two feet. If they’re running deeper than the depth set as everyone complains they do, we should nail her down near her keel. The book says she draws thirty-five feet.”
“Our book’s old,” Sirocco said.
“The battleship isn’t new. No matter how they’ve modernized her she’ll draw the same amount of water or more. When I start the sonar plot, the preliminary plot, I want you and Grilley to work on that at the gyro table in the Control Room where we can talk to each other. I’m going to have Edge and Botts with me in the Conning Tower. Edge can handle the TDC. He’s bright and quick. Botts can handle the periscope motors and read off the bearings to Edge. That’s about all the old man is good for. I’m thinking seriously of recommending he be given shore duty after this run.”
“The destroyer escorts, sir. How do you think they’ll deploy the twelve destroyers?”
“I’ve tried to put myself in the place of the commander of that destroyer squadron,” Mealey said slowly. “I served as Executive Officer on a destroyer once. I’ve tried to think as he would think. If I were in his shoes I’d put at least two, probably four destroyers out ahead of the battleship to make close in and distant sweeps, to clear out any submarine that might be lying in wait. I’d put two more ships aft for the same purpose. I think I’d put the remaining ships on either side of the battleship. But who the hell ever heard of using twelve destroyers to escort one battleship!”
“Let me continue to be the Devil’s Advocate, sir,” Sirocco said. “What happens to that sort of destroyer formation when the battleship nears the Northeast Entrance? We don’t know anything at all about that entrance but there’s bound to be some strong currents running through the reef, maybe even a strong tide. We don’t have tide tables, either. How will the destroyer commander use his ships? Will those ships out from sweeping go into the atoll itself?”
“I don’t think so,” Mealey said. “There’s no danger inside. The danger, if there is any and there is — we’re here — the danger will be outside. So I think his destroyers in the van will peel off the circle until the Big Boy is well inside. Then they’ll go in to the anchorage. “That’s when I intend to go under the destroyer screen, when they’re maneuvering and getting out of the way of the Big Boy so her Captain can take her in through the reef. There’ll be enough screws pounding away that they won’t be able to hear us.”