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by Rolfe L. Hillman and Thomas Lee

While most of the storied exploits of U.S. Navy (USN) submarine warfare in World War Two took place well outside of the Western Caroline Islands, the Western Carolines saw their share of action.
Located about 800 miles southwest of Guam, 500 miles east of the Philippines, and 1,300 miles south of the main Japanese islands, the Islands consist of Yap, Woleai, the Ulithi atoll, and the Palau island group, including Babelthuap, Peleliu, and Angaur.

Japan’s Presence
Japan acquired the Western and Eastern Caroline Islands, the Gilbert Islands, and the Mariana Islands minus Guam from the Germans after WWI. Japan made Truk its district HQ in the Eastern Carolines and Palau its district HQ in the Western Carolines. Palau also became Japan’s South Seas Bureau HQ.

In the 1930s, the Japanese developed the fishing, phosphate, and agricultural industries and built infrastructure in their new territories. They built a submarine base at Palau, as well as a military radio station on Yap and harbors, airfields, seaplane ramps, and military training bases throughout their Pacific holdings.

Strategic Value for Japan
The Western Carolines were of vital strategic importance to Japan. They were central to all of Japan’s Pacific island possessions and formed one layer in Japan’s Pacific defense-in-depth strategy.
Japan was almost entirely dependent on sea transport for acquiring the raw materials needed to fight the war. In the Western Carolines, Palau served as Japan’s convoy operations center for the region, transporting troops, materiel, and raw materials between the Home Islands and possessions in the Marshall Islands, the Eastern Caroline Islands, the Gilbert Islands, the Dutch East Indies, New Guinea, and the Solomon Islands.

Passing through the Western Carolines on merchant ships on their way to Japan were phosphates, metals, rubber, food, and other vital raw materials. In the other direction flowed troops, airplanes, spare parts, and technical experts. Palau also happened to be the Imperial Japanese Navy (IJN) forward submarine base for the region.

Parts of the Japanese forces that invaded the Philippines, Rabaul, and Guadalcanal in 1941 were launched from the Western Carolines. Palau was Japan’s district headquarters for the region, and after USN carrier and submarine operations destroyed the Japanese forces at Truk in February 1944, Adm. Koga relocated his headquarters westward to the relative safety of the island.

Japan’s War Goals
Japan’s plan was to destroy the U.S. Pacific Fleet at Pearl Harbor, conquer the resource-rich Indo China, Malaya, and Dutch East Indies, build up Pacific islands for defense against American reprisals, including taking Midway and thus isolating Hawaii, and then finish subduing mineral-rich China. Much of this was accomplished in the first six months following the attack on Pearl Harbor.

Japanese attacks on Australia, the British in Malaya and India, the Dutch in the Dutch East Indies, and the United States in the Philippines and Guam between December 1941 and April 1942 were intended to convey the sense that Japan’s forces were unstoppable. Their next goal was to negotiate peace with the Americans from a position of power and momentum with a cowed United States facing the specter of war in Europe. The Japanese would thus retain their newly expanded empire in the Pacific and avoid a long war.1

USN Submarine Operations
November 1942 saw the earliest USN submarine action in the Western Carolines. USS Seawolf (SS 197) and USS Seal (SS 183) were to pass through the Western Carolines from Fremantle on their way back to Pearl Harbor for overhaul. Seawolf arrived off Palau on November 11 to investigate reports of IJN aircraft carrier activity in the area. Upon her arrival, she spotted a carrier leaving Palau but was unable to gain attack position on it. Five days later, Seal got close to an IJN convoy near Palau and fired torpedoes at a freighter, Boston Maru (5,500 tons), before diving. One of the ships, possibly an escort, rammed Seal, which was followed by a depth charge attack until the convoy was safely away. Seal survived the encounter; Boston Maru did not.

The first sustained attention given by the USN to the Western Carolines was in late March 1944. U.S. forces under Gen. Douglas MacArthur were about to invade northern New Guinea and didn’t want the Japanese to provide air support to their troops there from air bases in the Palaus. U.S. carrier planes struck the Palaus on March 30-31, sinking or damaging 36 IJN surface ships and destroying about 160 airplanes. The carrier group then steamed past Yap and Woleai, attacking each in turn. During these attacks, codenamed Operation DESECRATE ONE, submarines USS Archerfish (SS 311), USS Bashaw (SS 241), USS Blackfish (SS 221), USS Gar (SS 206), USS Tang (SS 306), USS Tullibee (SS 284), and USS Tunny (SS 282) were stationed off Palau to intercept any IJN ships fleeing the attack; USS Dace (SS 247), USS Darter (SS 227), and USS Scamp (SS 277) were in position east of the Philippines to attack any ships escaping to Davao; and USS Harder (SS 257) and USS Pampanito (SS 383) were assigned lifeguard duty near Woleai and Yap.

USS Picuda (SS 382) was assigned to patrol the Western Caroline Islands on her first war patrol and, just past midnight on March 20, picked up by radar a small freighter with a single escort zig-zagging radically. Picuda spent the next two hours making an end-around run to get ahead of the ships, solving their zig-zag pattern to get their true course and speed as she went. Closing to within 1,300 yards, Picuda fired four bow torpedoes, the first two of which were observed to hit aft and amidships. Picuda went deep to secure for a depth charging that never came, and the crew heard a further explosion and the sound of Hoko Maru (1,504 tons) breaking up as she sank.

A day before Operation DESECRATE ONE, Adm. Koga, anticipating an airstrike on his new HQ at Palau, ordered his flagship, Musashi, to head for Davao in the Philippines to establish yet another headquarters. Tunny, however, was waiting just offshore and struck Musashi with a single torpedo. The torpedo put a 19-foot hole in Musashi’s bow, killing some of her crew and flooding her hydrophone compartment. While not sinking Musashi, Tunny’s torpedo sent her back to Japan for repairs.2 Only a week earlier, Tunny had sunk the IJN Type B2 submarine I-42 in the same area.

During the airstrike on Woleai, Harder’s crew made a daring rescue of a downed aviator who was within range of sniper fire from the shore. On April 13, an IJN destroyer, Ikazuchi, left the harbor at Woleai to search for Harder. Instead of diving, Harder’s skipper, Cmdr. Sam Dealey, closed to 3,200 yards, at which point Ikazuchi picked up Harder on sonar and charged. Dealey waited until Ikazuchi was 900 yards away before firing four torpedoes down the throat. Ikazuchi sank quickly, her survivors blasted by the armed depth charges that had been prepared for Harder.

sub rescue
USS Harder (SS-257) rescues Ens. John R. Galvin off Woleai Atoll. A Curtiss SOC
Seagull floatplane participated in the rescue.



On April 16, still lurking near Woleai, Cmdr. Dealey saw a single freighter leaving with two destroyers as escorts. Harder tracked the vessels until nightfall, at which point she surfaced to attack. Harder torpedoed and sank the freighter, Matsue Maru (7,000 tons). Harder then returned to Woleai to bombard Japanese positions with its 4-inch deck gun before returning to Fremantle.

After U.S. forces captured the Mariana Islands in August 1944, Adm. Ernest King, Chief of Naval Operations, thought that taking Formosa and bypassing the Philippines and the Western Caroline Islands would be better than Gen. Douglas MacArthur’s plan of slugging it out in the Philippines. Adm. King argued that, with Formosa in U.S. hands, USN submarines could effectively blockade Japan from getting oil and other commodities from Southeast Asia and leave troops outside the Japanese homeland stranded.3

Despite Adm. King’s arguments, the Joint Chiefs of Staff decided to go with Gen. MacArthur’s plan to invade the Philippines. This meant first taking Palau, the stated reason being to prevent IJN forces there from interfering with the upcoming invasion at Leyte Gulf. The invasion of the Palaus, which commenced on September 15, 1944, was codenamed Operation STALEMATE II. Instead of preventing merchant vessels from reaching Japan with much needed war resources, more than a dozen U.S. submarines were sent to patrol between the Philippines and the Western Caroline Islands during the invasion and saw no action.

Between Operations DESECRATE ONE and STALEMATE II, USN submarines were occasionally sent to patrol in Western Caroline waters.

About an hour before midnight on April 26, USS Trigger (SS 237) picked up by radar a convoy of what was believed to be five ships and an escort 14,000 yards away about 50 miles north of Palau. Over the following hour, Trigger paced the convoy to determine true course and speed and attain attack position. The convoy actually consisted of five large merchant ships, four of which were bunched in a tight group, with five escorts. Trigger had an ideal firing position between the escorts: the four bunched up freighters were overlapping and covered 20 degrees across her bow. At two minutes past midnight on the 27th, she fired all six bow tubes from 2,400 yards. The skipper observed two torpedoes hit the two nearer ships and heard two additional explosions hitting one or both of the two farther ships. One, Miike Maru, an 11,739-ton passenger-cargo ship, went down. Trigger relentlessly pursued the crippled convoy, making three additional attacks and claiming three additional freighters and one escort that were not confirmed by post-war IJN reports.

On April 27, USS Bluegill (SS 242), on her first war patrol, was southwest of Palau when she was spotted by the IJN cruiser Yubari. Yubari charged at Bluegill, according to the patrol report, “with large stern wake and bone in her teeth!” Bluegill fired her six bow tubes before diving. Two of the torpedoes found their mark, sinking Yubari.

On USS Aspro’s (SS 309) third war patrol, she departed from Pearl Harbor and searched for IJN ships in the Western Carolines before proceeding to Fremantle. Spotting an IJN convoy on May 15, she fired four torpedoes at a freighter, sinking Jokuja Maru (6,440 tons).

Just before dawn on May 25, USS Flying Fish (SS 229) surfaced near a convoy she had chased from just north of Palau and loosed four torpedoes at overlapping targets. Taito Maru (4,466 tons) and Osaka Maru (3,740 tons) burned for hours before their flames were extinguished by the enveloping sea.

On July 3, USS Albacore (SS 218) sank the 130-ton Taiei Maru, on its way from Yap to Palau, using her deck gun. Only five of Taiei Maru’s survivors agreed to be taken onboard by Albacore’s crew.4 USS Balao (SS 285) made good use of her 4-inch and 40mm deck guns during her sixth war patrol. On July 26, 1944, Balao bombarded Angaur Island, hitting a lighthouse, a loading dock, and a warehouse. On July 29, Balao joined USS Drum (SS 228) in a coordinated deck gun attack on two sampans until the Japanese abandoned ship and the sampans were destroyed.5

The only USN submarine lost in the Western Carolines is Tullibee. On March 26, 1944, while attacking a large troop transport north of Palau, one of her torpedoes malfunctioned and circled back on her, killing all but one of her crew.

USN Non-combat Submarine Operations
The U.S. submarines operating in the Western Carolines had other missions besides anti-shipping attacks. Several boats were assigned lifeguard duties to rescue aviators who went down in the water during the bombing of the Western Caroline Islands and later during the invasion.

Prior to the invasion of the Western Carolines, a few subs conducted close-up reconnaissance to aid the invasion planning. Seawolf took extensive photographs of the Palaus and recorded enemy radar positions and frequencies during this time. During the Palau blockade, USN submarines inserted frogmen to conduct beach reconnaissance of Peleliu and Angaur, and Seawolf, USS Permit (SS 178), and USS Burrfish (SS 312) were sent to take beach photographs.

On their own initiative, some submarine skippers would pick up downed Japanese pilots or search floating wreckage of ships they had sunk for survivors when the situation allowed for it. Survivors often were quite willing to provide information on Japanese troop strengths, shipping schedules, and minefield locations.

IJN Submarine Operations
The IJN’s primary submarine strategy was twofold: first, to conduct surveillance of enemy fleet units and bases and attack U.S. aircraft carriers, battleships, cruisers, and destroyers; a distant second were other missions, including anti-submarine warfare (ASW) and attacking U.S. lines of communication (LOC). Japan had envisioned a short war and did not have enough submarines in December 1941 (63 on December 7 with another 111 built during the war) to sufficiently interdict U.S. merchant traffic.6 Two of the IJN’s noteworthy submarine successes, however, occurred in the Western Carolines.

The first of these attacks began with a reconnaissance mission. On October 2, 1944, IJN submarines RO-46 (Kaichu Type) and I-177 (Type KD7) were ordered to reconnoiter the Ulithi atoll in preparation for the first Kaiten attack on the U.S. Third Fleet, which was anchored there. The Kaiten was part manned mini-submarine, part suicide torpedo.

On November 20, IJN submarines I-36 (Type B1) and I-47 (Type C2), each carrying four Kaitens on their decks, maneuvered into position just outside the atoll. Of the eight, only five were able to launch. Of those, just one found a target, fleet oiler USS Mississinewa (AO 59), which exploded and sank. The successful Kaiten pilot, Lt. j.g. Sekio Nishina, was a co-inventor of the Kaiten. Both I-36 and I-47 made their way back to Japan, where optimistic IJN after-action assessments determined that the mission accomplished the sinking of two aircraft carriers and two battleships.

The other successful IJN submarine attack in the Western Carolines occurred on July 30, 1945. IJN I-58, a B3-class submarine commanded by Cmdr. Mochitsura Hashimoto, torpedoed and sank USS Indianapolis (CA 35) west of Guam and Ulithi on its way to the Philippines after having delivered components of Little Boy, the nuclear bomb later dropped on Hiroshima.7

IJN submarines scored their share of victories against U.S. warships, sinking two aircraft carriers (Wasp, Yorktown), a carrier escort (Liscome Bay), a light cruiser (Juneau), four destroyers (Hammann, Henley, O’Brien, Porter), and two submarines (Corvina, Grunion) in the first two years of the war. They were not as successful later, however, because of the increasing effectiveness of U.S. ASW operations. Between September 25 and November 19, 1944, Japan lost submarines I-37, I-175, I-177, and I-364 in the Western Carolines to USN surface ships. Another factor that accounted for the IJN’s poor submarine performance was overly cautious skippers who declined to attack unless conditions were highly in their favor.

Chart graphics

In the Wake
In the Pacific theater, the USN had 51 submarines at the start of the war, lost 48, and had 153 remaining at war’s end. The IJN started the war with 63 ocean-going submarines, lost 118, and had 46 remaining at war’s end.

By the end of the war, USN submarines had accounted for more than 50 percent of IJN losses. The U.S. Submarine Force sank 1,178 merchant ships weighing 5,053,491 tons and 214 warships, including aircraft carriers, battleships, cruisers, destroyers, escorts, and submarines. By tonnage, only about 1 percent of these submarine successes were achieved in the Western Carolines.

Unfortunately, USN submarines’ contributions during the two major U.S. actions in the Western Carolines—the airstrike in late March 1944 and the invasion of Peleliu and Angaur in September 1944—were minimal. Over the objection of Vice Adm. Charles Lockwood, SUBSOWESPAC, Adm. Chester Nimitz, Commander in Chief, Pacific Ocean Areas, had ordered USN submarines to conduct operations in support of these actions that did not put them to their best use: eliminating IJN freighters, tankers, and transports.

Aside from their support in Operations DESECRATE ONE and STALEMATE II, U.S. submarines operating in the Western Caroline Islands relentlessly whittled down Japanese merchant shipping along their primary convoy routes east of the Philippine Islands. Following Operation STALEMATE II in fall 1944, the Japanese had to confine all of their merchant shipping to the East China Sea and the South China Sea. All IJN targets east of the Philippines had been eliminated, so U.S. submarines were
shifted to patrolling farther west and north to prevent Japanese reinforcements and supplies from
reaching the Philippines ahead of the invasion by U.S. forces under Gen. MacArthur.

Rolfe L. Hillman III of WBB currently works as a senior submarine training analyst supporting the OPNAV N973B Submarine Manning and Training Office in the Pentagon. Mr. Hillman, who graduated from Albion College in 1972 with a Bachelor of Arts degree/history major, has been a Navy support contractor since 1983.

Thomas Lee is a contractor at WBB supporting U.S. Navy N97 and is the managing editor of UNDERSEA WARFARE Magazine. He is a graduate of the E.W. Scripps School of Journalism at Ohio University.

End Notes

1 WW2 Pacific: Little Known Facts: Attacks and Threats on the US in WW2; US Possessions; Pearl Harbor,
Dec 7, 1941. http://www.ww2pacific.com/attacks.html.


2 C. Blair Jr., Silent Victory: The U.S. Submarine War against Japan, (Naval Institute Press, Annapolis, 1975,
p. 354).

3 Blair, p. 694.

4 uboat.net, Allied Warships, Albacore (SS 218). http://www.uboat.net:8080/allies/warships/ship/2964.html.

5 UNDERSEA WARFARE Magazine, Summer 2007, Vol. 9, No. 4, The Submarine Force’s Diversity Trailblazer, p. 33.
Also, Dictionary of American Naval Fighting Ships (DANFS), Balao. http://www.history.navy.mil/danfs/b1/balao.htm.

6 M. Sturma, Surface and Destroy: The Submarine Gun War in the Pacific, The University Press of Kentucky, 2012 (Reprint edition), p. 20.

7 M. Hashimoto, Sunk, Henry Holt, NY, 1954, p. 224. Also, M. Stille, Imperial Japanese Navy Submarines 1941-45, Osprey, Great Britain, 2007, p. 33.