Operation Hailstone

• 1. Introduction

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  Operation Hailstone struck Truk Lagoon on the 17th and the 18th of February 1944, and it dismantled one of the most feared myths in the Pacific War in less than two days. For years, American naval planners had spoken of Truk in hushed tones. They called it "the Gibraltar of the Pacific" and "the Japanese Pearl Harbor." It was supposedly a fortress so formidable that it could not be touched. What actually happened when U.S. Navy aircraft arrived over the lagoon shattered that reputation entirely.

  The questions this story raises are pointed ones. How did a base so central to Japanese naval power end up so poorly defended? Why were the biggest Japanese warships already gone when the Americans arrived? And what did the destruction of nearly 200,000 tons of shipping actually cost Japan in the years that followed?

• 2. The Myth of the Fortress

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  Japanese troops first occupied Micronesia, including the Caroline Islands, in 1914, and Truk was established as a naval anchorage as early as 1939. It grew into the home port of the Imperial Japanese Navy's 4th Fleet, known as the "South Seas Force," and later served as the Combined Fleet's forward operating base. Five airfields and a seaplane base were constructed there, making Truk the only major Japanese airfield within flying range of the Marshall Islands.

  Yet the intimidating image was largely hollow. The reality, as observers later noted, was that Japan's economic limitations prevented it from building both a large navy and extensive shore fortifications. It chose its naval forces and let fixed defenses go unbuilt. Serious work on Truk's fortifications did not begin in earnest until late 1943, and even then the effort fell short. Anti-aircraft guns were few, radar warning was inadequate, and the separate command arrangements for Navy fighter planes and Army troops made coordinated defense nearly impossible.

  American PB4Y-1 Liberator reconnaissance planes spotted the base in early February 1944, and that sighting accelerated a Japanese withdrawal that had been quietly underway since October 1943. Battleships, heavy cruisers, and carriers slipped out of the anchorage in the weeks before the attack, leaving behind a skeleton force of lighter warships and a crowded harbor full of merchant shipping.

• 3. The Strike

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  Admiral Raymond Spruance ordered Vice Admiral Marc Mitscher's Fast Carrier Task Force, designated TF 58, to carry out the assault. Three of the task force's four carrier groups committed to Hailstone, bringing five fleet carriers and four light carriers carrying more than 500 warplanes. Seven battleships, numerous cruisers, destroyers, and submarines rounded out the force.

  The IJN's 22nd and 26th Air Flotillas were on shore leave on the morning of the 17th of February, enjoying a rest after weeks on high alert following the Liberator sightings. The first American fighter sweep launched 90 minutes before daybreak, catching the garrison completely off guard. Radar at Truk could not detect low-flying planes, and the stations were understaffed regardless; telephone communications among defenders were poor. The result was total surprise.

  Japanese pilots scrambled minutes before TF 58 planes arrived over Eten, Param, Moen, and Dublon Islands. Of the more than 300 Imperial Japanese Navy Air Service and Imperial Japanese Army Air Service planes present, only about half were operational. American pilots in Grumman F6F Hellcats, flying with advantages of speed, altitude, armor, and surprise, cut down the defending Mitsubishi A6M Zeros one-sided. As many as 30 of the 80 Zeros scrambled in response were shot down. By the afternoon, almost no Japanese aircraft were airborne over Truk.

• 4. Ships Caught at Anchor

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  Grumman TBF Avenger torpedo bomber squadrons from Enterprise's Carrier Air Group 10 and Intrepid's CAG-6 opened the morning by dropping fragmentation and incendiary bombs on runways at Eten Island and the seaplane base on Moen Island. Dozens of aircraft were destroyed or damaged on the ground before the day's main strikes against shipping even began.

  Lieutenant Commander James D. Ramage, commanding officer of Dive Bombing Squadron 10, is credited with sinking the tanker Hoyo Maru. A more spectacular loss came when Lieutenant James E. Bridges and his Avenger crew from Intrepid's Torpedo Squadron 6 scored a direct hit on an ammunition ship. The torpedo detonated the vessel's bow ammunition, triggering a tremendous explosion that sank the ship instantly, killing 945 crew and passengers, and engulfed Bridges' own plane in the blast.

  Merchant vessels that tried to flee the lagoon ran into American submarines waiting outside. Those that attempted to escape through the atoll's North Pass faced repeated aerial attack and the guns of Task Group 50.9, which circumnavigated the entire atoll while bombarding shore positions. Auxiliary cruiser Akagi Maru was sunk by air attacks during this phase. Shipping losses for the operation ultimately totaled almost 200,000 tons, representing nearly one-tenth of all Japanese shipping losses recorded between the 1st of November 1943 and the 30th of June 1944.

• 5. Spruance's Surface Battle

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  Reports of Japanese warships fleeing through the North Pass reached Admiral Spruance mid-battle, and he did something that unsettled some of his own staff. Rather than leaving the work to aircraft, he personally took tactical command of Task Group 50.9 and drove his surface force into the fight. That group consisted of heavy cruisers Minneapolis and New Orleans, four destroyers, and the new battleships Iowa and New Jersey.

  The group targeted a cluster of already-damaged Japanese ships: the cruiser Katori, auxiliary cruiser Akagi Maru, destroyers Maikaze and Nowaki, and minesweeper Shonan Maru. Yorktown's bombers had already claimed two hits on the maneuvering Katori and hits on other ships; Essex bombers claimed five hits on one vessel, leaving it stopped dead in the water. The battered ships had little answer for Spruance's battleships.

  New Jersey's 5-inch guns combined fire with American cruisers to sink Maikaze and Shonan Maru. Iowa targeted Katori, already dead in the water, and finished her with hits from the main battery. The sole survivor of the group was the destroyer Nowaki, which sailed through fire from both battleships and escaped with only minor damage from a straddle by a 16-inch round fired by New Jersey at the extraordinary range of 35,700 yards, equal to 20.3 statute miles. The engagement holds a specific distinction in naval history: it was the only time Iowa and New Jersey fired their main guns at enemy ships. The Japanese destroyer Maikaze did manage to fire torpedoes at New Jersey during the exchange, but they missed.

• 6. The Night Raid and the Intrepid

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  Japanese retaliation came after dark, in the form of small groups of bombers probing the task force's defenses from roughly 21:00 on the 17th to just after midnight on the 18th of February. At least five groups of between one and three enemy planes attempted to reach the fleet carriers past the screening ships.

  One aircraft succeeded. A lone Rikko-type twin engine bomber from the 755th Kokutai, known as the Genzan Air Group, attacked Task Group 58.2 and put a torpedo into the starboard quarter of Intrepid, damaging her steering and killing 11 sailors. Intrepid withdrew from the combat zone and did not return to action until August 1944.

• 7. What Hailstone Actually Cost Japan

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  American carrier aircrews came away disappointed that the major Japanese surface warships were gone when they arrived. The only warships remaining were two light cruisers, four destroyers, and some auxiliaries; the capital ships had been pulled out months earlier. But the damage to Japan's logistical network was severe in ways that did not immediately show on a ship count.

  Some 17,000 tons of stored fuel were destroyed by American airstrikes. Among the sunken vessels were several fleet oilers, a class of ship the Japanese navy was running short of by early 1944. The comparison to Pearl Harbor is instructive: when Japanese aircraft struck Pearl Harbor on the 7th of December 1941, they left the base's oil storage tanks and repair yards untouched. At Truk, the Americans destroyed both. And unlike the United States after Pearl Harbor, Japan's industrial output could not replace what was lost at Truk.

  The Imperial Japanese Navy General Staff responded by blaming Admiral Masami Kobayashi and relieving him of command two days after the attack. On the 30th of May 1944 he was forced from active service, and the following day he was transferred to the reserves.

  The seizure of Eniwetok, which Hailstone was designed to protect, combined with the neutralization of Truk to open the path to Saipan. Once Saipan fell, U.S. land-based heavy bombers sat within range of the Japanese home islands for the first time in the war. The cascading effect of severed supply lanes was visible at the Battle of Leyte Gulf in October 1944, when IJN forces were forced to sortie separately from Japan and Lingga Roads because fuel constraints left them unable to concentrate as a single fleet.

• 8. Truk After the Battle

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  Between 70 and 120 Japanese aircraft flew from Rabaul to Truk on the morning of the 19th of February, the day after the operation ended, as the Japanese command pulled its remaining airmen out of Rabaul following the Allied island-hopping campaign that had cut it off. The mechanics who tried to follow on the 21st of February were not so fortunate; their ship was sunk by Allied bombers before it reached Truk.

  Spruance sent carrier planes back on the 29th of April to hit the base again, destroying more aircraft, ground facilities, and air defenses. American air units then conducted regular reconnaissance and raids on Truk through the rest of the war, ensuring it was never rebuilt into an operational threat. In June 1945, British forces struck Truk in Operation Inmate, using cruisers and carrier-based bombers to gain Pacific combat experience before more demanding operations against the Japanese home islands. Historian David Hobbs described Truk at that stage as having been "reduced to starving impotence."

  The garrison's situation grew desperate. Imperial Japanese Army reinforcements who had arrived before Hailstone strained the food and medical supply chain. After the Palau Islands were captured by American forces in September 1944, almost no resupply reached the atoll. The garrison turned to growing its own food, a task made harder by tropical conditions and the ongoing damage from air attacks. Most personnel became malnourished and disease-ridden. Despite this, the garrison held enough ammunition when the war ended in August 1945 to supply its gun batteries for at least 30 days of combat. Truk's formal surrender took place on the 2nd of September 1945, aboard ship, the same day Japan signed the general surrender documents, and the garrison's survivors were repatriated in November and December of that year.