At 8:30 A.M. on June 15, 1944, members of the 6th, 8th, 23rd, and 25th Marine regiments landed on  

the southwest shores of Saipan, commencing the US invasion of the Marianas Islands.  

It took much longer to pacify the Marianas than Admiral Chester Nimitz expected.  

On July 9, after three weeks of hard fighting, Marines and the men of the 27th Infantry Division  

finally declared Saipan secured, but at the cost of 3,426 Americans killed in action. After that,  

in late July, the amphibious assault turned toward the islands of Guam and Tinian. U.S. forces did  

not pacify those islands until August, at the cost of another 2,109 American lives. Consequently,  

for the whole summer, VADM Raymond Spruance’s 5th Fleet had to remain tethered to thosee islands  

to ensure the success of this important mission. But as the landing occurred, the Japanese were  

on their way. With 62 ships, Vice Admiral Jisaburō Ozawa’s Mobile Force departed the Philippines with  

the intent of carrying out Order 73, the execution of a decisive battle against the American fleet. 

The Japanese were optimistic of success. The Combined Fleet’s Chief of Staff, Ryonosuke Kusaka,  

believed that Ozawa had timed his operation perfectly. The Japanese carrier force would  

strike the Americans when it was too late for them to call off their landings, but also far too early  

for them to have achieved any success on the islands. “The enemy would be in a fix,” Kusaka  

wrote, “having no choice but to try and save their own soldiers.” When Ozawa sprang his trap,  

the Americans would have nowhere to retreat. But in the end, it didn’t happen that way,  

largely because the Americans received helpful intervention from their submarine fleet. 

By the time Operation Forager began, the US Navy’s submarine command, called SUBCOMPAC,  

had 48 boats deployed at sea. The summer of 1944 proved to be an ideal time for submarine  

commanders to show what they could do. For the first 22 months of the war, their boats  

had suffered from defective torpedoes. Not until the autumn of 1943 were these problems rectified.  

Further, the Pacific submarines had more bases from which they could operate,  

allowing them to move farther into Japanese waters and provide crucial reconnaissance information.  

These two changes made US submarines a powerful factor in the Battle of the Philippine Sea. 

Submarines spotted Ozawa’s ships as soon as they set sail. On June 10, at 9:10 A.M., in the  

waters off Tawi Tawi, USS Harder made contact with a Japanese surface force. After enduring  

a depth charge attack, the crew radioed their information to SUBCOMPAC. Three days later, USS  

Redfin witnessed another portion of Ozawa’s fleet as it emerged from its anchorage. Scanning through  

the periscope, LCDR Marshall Austin could see six aircraft carriers, four battleships, six cruisers,  

and six destroyers. Austin could not get his boat into a suitable position to fire a torpedo,  

but after the Japanese ships left the area, he also surfaced and sent a detailed contact report. 

On the evening of June 15, yet another US submarine, USS Flying Fish, sighted these  

same Japanese ships heading through San Bernardino Strait. Finally, 200 miles east of Surigao Strait,  

USS Seahorse came across another element of the Japanese fleet, VADM Matome Ugaki’s  

Battleship Division. Due to the darkness and the distance between the submarines and the fleet,  

neither Flying Fish nor Seahorse could fire torpedoes, but the information gave Spruance  

a clearer picture of Japanese intentions. Even though these big groups of Japanese  

ships escaped torpedoing, another submarine encountered a small element of Ozawa’s advance.  

At 11:30 P.M., June 15, USS Cavalla—a brand new submarine on its first wartime patrol—caught  

sight of four Japanese ships—two destroyers and two oilers. This was Ozawa’s refueling convoy.  

Cavalla’s commander, LCDR Herman Kossler, took the submarine to radar depth and lined up a shot.  

Suddenly, one of the destroyers changed course and headed straight toward his periscope.  

Believing he’d been spotted, Kossler ordered his boat to submerge to 75 feet and the Japanese  

destroyer passed right over it, not pinging or dropping any depth charges. Fortunately, the  

destroyer had not seen Cavalla’s periscope, but had simply made an unexpected course correction.  

After the Japanese ships left the area,  Kossler surfaced and reported his sighting.  

He intended to make haste for San Bernardino Strait to relieve USS Flying Fish, but the  

commander of SUBCOMPAC, RADM Charles Lockwood, believed that Kossler needed to follow the oilers.  

They might be going to a refueling rendezvous, which meant big game ahead. Lockwood advised,  

“Trail. Attack. Report. Keep your chin up.” For the next three days, Cavalla pursued  

the oilers. After dark on June 18, the  sonar picked up new surface contacts.  

The sonarman determined that there were at least fifteen ships. Clearly, the oilers had  

rendezvoused with another part of the Japanese fleet. Kossler considered making a night attack,  

but in the end, he believed it wiser to keep his distance, stay on the surface, and make a report.  

When the Japanese ships steamed out of sight, most of the crew on Cavalla were in a foul mood.  

Twice, they had missed an  opportunity to fire a torpedo.  

But after delivering this last report, Kossler ordered his submarine to continue the pursuit. 

Kossler’s decision to report  his findings paid dividends.  

In the end, it enabled another  submarine to come to his assistance.  

After Kossler sent his first contact report,  SUBCOMPAC dispatched three more submarines to  

the area. Based on the helpful information  sent from the second contact report,  

one of them, USS Albacore, managed to put itself into the path of the Japanese Mobile Force.  

Not only that, but the crew of the Albacore  found itself targeting Taihō—Ozawa’s  

flagship—a mammoth, 37,000-ton fleet carrier out on its maiden voyage. At 7:45 A.M. on June 19,  

from a range of 5,300 yards, LCDR James  Blanchard aimed his boat at Taihō and fired all  

six bow torpedoes. At that moment, Taihō had just begun launching aircraft, sending them on  

a mission to find and destroy the American fleet. One of the fighter pilots, Warrant Officer Sakio  

Komatsu, saw the trail of bubbles heading  toward his flagship. Without hesitation,  

he keeled his plane into a crash-dive and slammed his aircraft into the first torpedo,  

exploding it, and killing himself in the process. Albacore’s next four torpedoes missed astern,  

but the last one struck right in the middle of Taihō’s starboard side. The torpedo punctured the  

carrier’s massive aviation gas tanks, and soon, toxic fumes began spreading throughout the ship. 

The torpedo’s damage had been fairly light, but after several hours, the spreading av-gas fumes  

made it impossible for the carrier to continue flight operations. Around noon, Taihō’s damage  

control officer made an unwise decision to vent the gas. He switched the ventilation system to  

full capacity and ordered all doors and hatches opened. But instead of venting the air, this  

decision pushed the vapor into the damaged section of the ship, where it ignited. About 12:30 P.M.,  

more than five hours after the torpedo hit,  Taihō erupted like a volcano, killing more  

than half its crew. Ozawa survived the explosion and evacuated to a nearby cruiser. Hours later,  

the stricken ship sank stern first,  taking 1,650 crewmen to a watery grave. 

Taihō was not the only Japanese carrier lost to an American submarine on June 19.  

By late morning, LCDR Kossler and USS Cavalla reached the scene as well. In fact,  

Kossler had just about given up the chase. He had decided to return to his original mission  

to head to the Philippines. But three hours  into the journey, his boat came across Ozawa’s  

task force, which was then in the midst of  recovering aircraft from its first airstrike.  

Through the periscope, he targeted the 32,000-ton fleet carrier Shōkaku, which was steaming  

slowly—left to right—across Cavalla’s path. Ensign Ernest Zellmer was Cavalla’s  

communications officer. He occupied the plotting desk in the starboard corner of the submarine’s  

conning tower. He watched intently, as his skipper meticulously tried to identify the Japanese ships. 

"Over the horizon came a carrier, two cruisers, and a destroyer. Cavalla headed toward the targets.  

The carrier was taking on planes and a  number could be seen stacked on the bow.  

The Captain did not know where Task Force 58 was; it was imperative that this target be positively  

identified before shooting. He did not want to torpedo a US carrier. The recognition manual of  

Japanese ships was checked and rechecked, but the carrier could not be positively identified.  

The angle on the bow was small and the range still large. The Executive Officer and the Fire  

Control Officer took looks through the scope, but uncertainty remained. Cavalla was getting closer  

and the Captain would soon have to make his decision. Cavalla avoided the destroyer  

between her and the carrier. Decision time was getting very close. Kossler raised the periscope;  

he was closer and the angle on the bow of  the carrier was larger. Now he could see  

the Japanese ensign – positive identification!" Kossler submerged his boat and closed to within  

1,200 yards. At 11:18 A.M., he ordered  all six bow torpedoes fired. As soon as  

the sixth torpedo left its tube, he took his  submarine deep and rigged for silent running. 

Three of Cavalla’s torpedoes struck  Shōkaku on the starboard side,  

one on the bow and the other two under the island structure. The fires burned out of control. Since  

the carrier had just recovered its aircraft, aviation gas was flowing through its pipes in  

the exact areas where the torpedoes struck. Gas spewed from the ruptured tanks and caught fire.  

The ammunition exploded, the boiler rooms flooded, and the ship lost speed and began to list.  

Then, at 2:08 P.M., an aerial bomb on the  hangar deck caught fire and exploded. This  

touched off four larger explosions, which caused the carrier to shiver apart. The ship went down,  

nose first, and the stern jutted high into  the air, exposing the screws to daylight.  

Although three destroyers managed to rescue 570 men, another 1,272 went down with the ship. 

Meanwhile, Japanese destroyers closed in on Cavalla’s position. For three hours,  

they dropped depth charges. Ensign Zellmer, the young communications officer in the conning tower,  

remembered those frightening moments: "The most frightening thing was that dive after  

attacking the Shokaku when the first two depth charge salvos caused the boat to become heavy.  

The destroyer dropped two series of depth charges as Cavalla was passing 75 feet. They  

were very close. Cavalla’s main induction line was flooded, making Cavalla about 12 ½ tons heavy.  

A sticky valve allowed a tank to overflow into the forward torpedo room bilge, making Cavalla  

even heavier, and gave her an exaggerated down angle. She was descending faster than intended.  

Before Cavalla’s descent was stopped, she was about 100 feet below her test depth of 312 feet.  

It had been necessary to increase the speed (and the noise) and maintain an up angle on the boat  

to check Cavalla’s dive and to hold her at 400 feet. Cavalla could not pump out any of the water;  

the pumps were noisy and would help the destroyers in locating us. From 300 to 400 feet was my most  

frightening time. I was at the plotting desk  in the conning tower, my battle station.  

I couldn’t see what was going on below and could not be of any help. I knew we didn’t dare blow  

any tanks because that would send bubbles up to the surface. For three hours the destroyers  

sought Cavalla; 105 depth charges were dropped. About 2 ½ hours after the attack, sonar reported  

large explosions and continuing noise for many seconds in the general direction of the attack. We  

interpreted those sounds as the death knell of the carrier—and we were right. The morale on Cavalla  

soared from the depths to which it had sunk after failing on our first attack against the convoy."

At night, Cavalla surfaced slowly. The boat was in bad shape. The sound gear was knocked out  

of commission, the main induction pipes were flooded, and the hull ventilation system was  

damaged. Kossler’s boat tilted at a four-degree up-angle merely to hold steady. But thankfully,  

the enemy was nowhere to be seen. The crew didn’t know if the carrier had somehow shrugged  

off the torpedoes or had gone to the bottom, but Kossler felt certain it had been the latter. He  

promptly sent a message to SUBCOMPAC: "HIT SHOKAKU CLASS CARRIER WITH THREE  

OUT OF SIX TORPEDOES . . . RECEIVED  105 DEPTH CHARGES DURING THREE HOUR  

PERIOD . . . HEARD FOUR TERRIFIC EXPLOSIONS IN THE DIRECTION OF TARGET TWO AND ONE HALF HOURS  

AFTER ATTACK . . . BELIEVE THAT BABY SANK." On June 19, the Silent Service had done an  

incredible job, informing VADM Spruance of the impending danger and knocking out two fleet  

carriers. Albacore and Cavalla had struck the most damaging blow to Ozawa’s plan, reminding the  

Japanese that the Americans were just as fearsome beneath the waves as they were above them.