Hellcats (12 page)

The physical installation itself consisted of several components. They included two soundheads, one of them a transmitting projector, the other a receiving hydrophone. Both were mounted on a rotating, retractable shaft enclosed in a thirty-one-inch-long, twelve-inch-diameter rubber sleeve filled with castor oil.
¹
In the
Spadefish
, the shaft from the forward torpedo room ran through the ship's pressure hull on the port side up to the main deck. She was the only sub to have a deck-mounted unit. Later, experience dictated that FM sonar soundheads mounted below a submarine's keel provided better signal propagation out ahead of the sub, which enhanced the sub's ability to locate mines. It also allowed for the use of FM sonar when the sub was running on the surface.

Another component consisted of a four-foot-tall equipment stack inside a steel box mounted to the forward torpedo room deck against the ship's curved hull. The stack contained an FM oscillator, a power amplifier, a receiver, and an analyzer. Another component, a hoist-training mechanism, turned, raised, and lowered the soundhead. A plan position indicator—or PPI scope—mounted in the sub's control room had a circular cathode ray tube similar to a radarscope. Like a radarscope, the PPI scope had a long persistence screen that inhibited image ghosting, a sweep-around circuit, and the necessary power controls to turn it on and off. Distances and relative bearings necessary to navigation were scribed on the face of the PPI scope. A loudspeaker mounted in the conning tower above the FM sonar operator's position sounded a bell-like tone that warned of impending contact with mines. There were also various junction boxes and the necessary connective cabling between the conning tower and forward torpedo room.

Aboard a sub feeling its way through a minefield, FM sonar displayed the returning sonar echo from a mine contact on the PPI scope as a bright green spot of light shaped like a pear.
²
The sharper the pear, the closer the mine. The pearlike display was augmented by the aforementioned bell tone, the volume and clarity of which were directly proportional to the distance from the sub to an actual mine. The bell tone, dubbed “hell's bells” by submariners, and the display of green pears gave the sonar operator a bird's-eye view of the position and range of each contacted mine relative to the submarine. Unlike standard sonar gear, with its individual and discontinuous pulses of sound that often required up to eight minutes for a full 360-degree scan, FM sonar, with its continuous modulated signal, could conduct a 360-degree scan in only eight seconds. In addition, FM sonar's ability to rapidly sweep an area for targets made it difficult for the Japanese to detect its pulse via their conventional single-channel listening gear.

In tests FM sonar sweeps from as far away as eight hundred yards gave good returns from dummy mines in the form of bright green pears and clear, pure bell notes, while poor returns from, say, kelp or schools of fish usually gave off an indistinct green pear and a mushy bell tone, a result of their indefinite shapes. The combined visual display and audio warning allowed a sub to find gaps between rows of mines swaying at the ends of their anchor cables. Or so the theory went. The trick was to thread this forest of mine cables while submerged, no easy feat. After all, mines that are surrounded by cubic miles of seawater are relatively small objects that give off correspondingly weak echoes that can be masked by sound reverberations caused by shallow water, an uneven seabed, and, up above, rough seas. Tests conducted on dummy mines and on triplanes—underwater devices equipped with three perforated sound-reflecting “wings”—revealed just how temperamental the gear could be and how much time and patience it took for the UCDWR scientists to fix problems both mechanical and electronic.

While the
Spadefish
was outfitted with FM sonar, her sonar men underwent special training to learn how to operate the gear and how to interpret those green blobs and bells: Were they mines, kelp, or fish? If they got it wrong, the
Spadefish
wouldn't stand much of a chance if she got tangled up in a row of Japanese mines.

As for her crew of motor macs, electrician's mates, and the like, they weren't impressed with FM sonar and its purported ability to locate mines. So far it hadn't worked as advertised, when it worked at all. And anyway, hunting mines was a job for minesweepers, not submarines. Things went so badly with it that the equipment finally had to be removed for repairs at UCWDR's lab, after which it was delivered back to Mare Island, where it caught up with the
Spadefish
completing her fitting out for war patrols. As scuttlebutt spread through the sub force that more submarines were going to be equipped with FM sonar, sub sailors took a dim view of what might be in store for them. Back in Pearl, Lockwood sifted through the daily reports submitted by Dr. Harnwell, Dr. Henderson, and by SubPac's liaison officer in San Diego, who had his ear to the submarine grapevine. Lockwood discovered just how controversial this new gadget was and how little enthusiasm for it there was among submarine sailors. Lockwood knew that he had to convince both officers and enlisted men to get on board with FM sonar or there'd be no mission to the Sea of Japan. The only way to do that was to perfect the damned thing and then prove that it worked. If he couldn't do it, he'd never put together a task force of submarines to tackle the job he had in mind.

 

 

The
Spadefish
arrived at the
submarine base at Pearl Harbor in late June. No sooner had she tied up than Lockwood and Voge crossed the brow for a conference with Underwood. The two senior officers peppered the skipper with questions about his experience with FM sonar in tests at San Diego.

Underwood's report wasn't particularly encouraging. Tests of the
Spadefish
's equipment conducted on dummy mines off the coast of California had been disappointing. FM sonar had failed to register mine contacts visually on the PPI scope or audibly by hell's bells. Sometimes the unit couldn't detect targets at all or had a hard time differentiating between solid objects and schools of fish. It wasn't reliable, said Underwood. Vacuum tubes burned out and wiring overheated. Repairs often took hours. If Lockwood expected submariners to trust this gadget when it came time to locate real mines, he had another thing coming. This wasn't what Lockwood and Voge wanted to hear, but they took the news in stride. Lockwood the optimist believed that he, his men, and the scientists at UCDWR were pioneers in the business of submarine mine hunting and, like any new venture that relied on unproven technologies, it would take time to flush the bugs and gremlins out of the sonar units coming from UCDWR's labs.

In the event, UCDWR technicians who had gone on ahead to Pearl to meet the
Spadefish
gave her FM sonar a thorough going-over. They also supervised some needed voyage repairs—heavy seas had bent the deck-mounted transducer's shaft—after which they pronounced the system ready for duty.

Lockwood put to sea in the
Spadefish
on July 13 to experience firsthand a full-scale test of FM sonar, not on a live minefield but on a dummy minefield planted by the Navy's mine force in the deep waters off Barbers Point, Oahu.

Employing recent intelligence about Japanese mines and minefields collected by JICPOA (ICPOA had been renamed Joint Intelligence Center, Pacific Ocean Areas), the mine force had sown the dummies to replicate an enemy field. Lockwood believed that submarines attempting a penetration of the Sea of Japan would encounter such fields and that familiarity with their layout would provide the submariners the experience and confidence to make a clean run through them.

The Japanese employed a moored spherical, horned contact mine known as a Type 93. Weighing 1,500 pounds, it was filled with 220 pounds of TNT plus a pusher, usually powered aluminum, to increase the mine's explosive force. Later models had up to nine sulfuric acid-filled horns protruding from the mine's cast-iron surface. When a ship hit a horn, it would break open, releasing acid, which energized a battery and set off the detonator. Japanese mines were usually sown in two or three rows across shipping lanes or, in the case of the Sea of Japan, across straits of entry, the rows spaced four hundred to a thousand yards apart. A gap of seventy-five to a hundred yards separated each mine from its neighbors to prevent an explosion from setting off the other mines in the string by chain reaction.

The mines making up a field were generally planted no deeper than a hundred feet, often in three tiers ranging from ten feet to forty feet to seventy feet. A minefield's effectiveness is reduced somewhat by “mine dip,” which occurs when deep-water currents push cable-moored mines in the direction of the current flow several feet lower than their planted depth. This so-called “dip gap” gives passing ships a greater margin of safety than they would otherwise have had. Such was the case when Ray Bass ran the
Plunger
through La Pérouse Strait during that early foray into the Sea of Japan. As Bass discovered, mine dip may have accounted for the fact that he and his crew were still alive and their sub in one piece. Even so, Bass's blind run through La Pérouse was thought to be far too dangerous for any submarine to attempt it again. Experience would prove otherwise.

As for those floaters often sighted by patrolling submarines, international agreements stipulated that mines were to be armed only when the weight and tug on the mooring spindle armed the detonator. Otherwise the mine was supposed to self-sanitize, that is, render itself harmless. No one trusted the Japanese to abide by such agreements, so submarines gave floating mines a wide berth. Moored or not, the assumption was that the Japanese had planted thousands of mines in waters bordering Japan to protect the home islands from invasion from the sea. As long as U.S. submarines operated in those mined waters, Lockwood had to hope that FM sonar, aside from facilitating a raid on the Sea of Japan, would reduce the risks that mines posed to submarines engaged in regular war patrols.

 

 

Lockwood's ride on the
Spadefish
was an opportunity to gauge FM sonar's sensitivity and accuracy for himself. UCDWR technicians, some stooped with fatigue from the late nights spent tearing apart, repairing, testing, and reassembling the
Spadefish
's unit, declared it was fully functional again. Lockwood, and especially Underwood, expected to see a vast improvement over its performance in California.

Approaching the dummy minefield off Oahu, Underwood gave the order to submerge: “Clear the bridge! Dive! Dive!”

Two honks of the Klaxon diving alarm sent the men into action. Lockwood and the four lookouts, followed by Underwood, scrambled down the ladder from the bridge to the conning tower below, the eight-foot-by-twelve-foot horizontal steel cylinder set above the ship's control room. Every inch of space inside was taken up with periscopes, FM sonar gear, radar scope, sonar stand, and the TDC. Underwood, his exec, the quartermaster of the watch, the helmsman, sonarman, telephone talkers, and now ComSubPac shouldered around one another trying to make room.

The OOD, the last man down, slammed the hatch shut and dogged it. “Hatch secured, sir.”

The hammer of diesel engines ceased as propulsion shifted to the batteries. A litany of orders and repeat-backs resounded between the conning tower and control room. “All ahead full! Rudder amidships! Five-degree down bubble!” In the control room the chief of the watch promptly closed the outboard and inboard engine exhaust valves and main induction. Scanning the red-and-green-lit Christmas tree hull opening indicator panel, the chief reported, “Green board; pressure in the boat.” The main ballast tank vents popped open with a
whoosh!
as the chief, his hands a blur, pulled the hydraulic vent valve control levers open one after another. Seawater flooding her ballast tanks, the
Spadefish
started to submerge. A landlubber might have thought he was witnessing pure chaos but in fact it was a series of practiced evolutions required to submerge the
Spadefish
in thirty seconds.

Underwood, looking down into the control room through the open hatch in the conning tower's deck, ordered, “Make your depth six-five feet.”

The diving officer confirmed the order. “Six-five feet, aye.” Lockwood, the deck under his feet angling down, held on and leaned away from the dive. He was in his element, among fellow submariners aboard a fleet sub.

The two men seated at the diving stand in the control room muscled the big nickel-plated wheels controlling the
Spadefish
's bow and stern planes. As the
Spadefish
approached sixty-five feet—periscope depth—the diving officer asked for two-thirds speed, then ordered, “Blow negative to the mark!” Dewatering negative tank restored the sub's neutral buoyancy and helped trim the ship for submerged operations. Then, “Ease your bubble.”

Underwood motioned for the periscope. The quartermaster yanked the hydraulic control lever in the overhead. The scope hummed out of its well, jerked to a stop at its upper limit. Underwood made a quick 360-degree scan. Satisfied that the area was clear of ships, he turned the scope to the marker buoys dead ahead, where the minelayers had sown a dummy field. “Coming up on the mine plant.”

Satisfied that he'd demonstrated for his three-star boss how tight a ship he ran, Underwood ordered, “All ahead one-third. Stand by on FM sonar.”

Lockwood hovered near the PPI scope, watching over the operator's shoulder. He saw a circular glass screen with concentric rings, like ripples from a stone dropped into a pond. The rings indicated ranges from one hundred yards to several thousand yards. Bearing lines, like the spokes of a wagon wheel, extended across the scope's face to all points of the compass. The circles and spokes allowed an operator to plot the position of any mine contacts relative to the position of the
Spadefish
. A thin, luminous line swept continuously around the circumference of the scope: If the sonar beam made contact with a mine, the contact would blossom into a bright green pear every time the line swept past its position.