Operation Hailstone
In 1939, Japanese troops established Truk Lagoon as a forward operating base for the Imperial Navy's 4th Fleet. By 1944, American leaders called it the Gibraltar of the Pacific or the Japanese Pearl Harbor. This nickname suggested a heavily fortified stronghold ready to repel any invasion force. The reality was far different from the public perception held by U.S. Navy commanders and citizens back home. No significant reinforcements arrived at Truk before the war intensified in early 1944. Defensive measures against land attacks only began in earnest during late 1943. Shore batteries were erected and airfields extended, but these preparations remained inadequate. Few anti-aircraft guns protected the anchorage while radar warning systems failed to detect low-flying aircraft. Communication lines between naval fighter planes and Army troops suffered from separate command arrangements that hindered coordination.
Admiral Raymond Spruance ordered Vice Admiral Marc Mitscher's Fast Carrier Task Force to raid Truk on the 17th of February 1944. Intelligence reports indicated that aircraft stationed at Truk could interfere with the upcoming invasion of Eniwetok. Recent sightings of U.S. Marine Corps PB4Y-1 Liberator reconnaissance planes had accelerated the withdrawal of major units from the anchorage since October 1943. Three of four carrier task groups committed over 500 warplanes to the operation. Five fleet carriers and four light carriers formed the core of this massive striking force. Supporting them were seven battleships plus numerous heavy cruisers, destroyers, and submarines. The Japanese understood their weakness and had begun withdrawing ships as early as the first week of February 1944. This effective abandonment of Truk as a forward base preceded the American attack by days.
U.S. carrier aircraft launched their first fighter sweep ninety minutes before daybreak on the 17th of February 1944. No Japanese air patrol was active because the IJN's 22nd and 26th Air Flotillas enjoyed shore leave after weeks of high alert. Radar stations failed to detect low-flying planes due to technical limitations and poor staffing levels. Telephone communications within the lagoon remained unreliable throughout the morning hours. Japanese pilots scrambled into cockpits just minutes before TF 58 planes arrived over Eten Island and Param Island. More than 300 Imperial Japanese Navy Air Service and Imperial Japanese Army Air Service planes sat at Truk that first day. Only about half of those aircraft were operational compared to over 500 functional planes aboard U.S. carriers. Grumman F6F Hellcats achieved a one-sided victory against Mitsubishi A6M Zero fighters flying below them. As many as thirty of eighty Zeros sent up in response were shot down during the initial battle.
Grumman TBF Avenger torpedo bomber squadrons from Enterprise Carrier Air Group 10 dropped fragmentation bombs on runways at Eten Island. Dive bombers cratered facilities while destroying hangars at the seaplane base on Moen Island. Lieutenant Commander James D. Ramage commanded Dive Bombing Squadron 10 when he sank the merchant tanker Hoyo Maru. Lieutenant James E. Bridges led an Avenger squadron that scored a direct hit on an ammunition ship named Hakuyo Maru. The resulting explosion took down 945 crew members and passengers while engulfing Bridge's plane too. Multiple air groups attacked a group of warships including cruiser Katori, auxiliary cruiser Akagi Maru, destroyers Maikaze and Nowaki, and minesweeper Shonan Maru. Yorktown dive- and torpedo-bombing squadrons claimed two hits on the violently maneuvering Katori. Essex bombers stated they stopped another cruiser dead in the water after five hits. Akagi Maru was sunk by air attacks before it could escape through the lagoon's North Pass exit.
Admiral Spruance put himself in tactical command of Task Group 50.9 to engage fleeing Japanese ships directly. His force included four destroyers, heavy cruisers Minneapolis and New Orleans, and battleships Iowa and New Jersey. Staff members viewed this decision as needlessly reckless since aircraft likely could have achieved similar results without risk. The battered Japanese ships did not stand much chance against Task Group 50.9 during the surface engagement. Japanese destroyer Maikaze managed to fire torpedoes at the battleship New Jersey but missed completely. U.S. Navy surface combatants received virtually no damage throughout the entire encounter. This marked the only time Iowa and New Jersey fired their main armament at enemy ships during their careers. New Jersey's 5-inch guns combined fire with U.S. cruisers to sink Maikaze and Shonan Maru. Nowaki escaped sailing through a gauntlet of fire from Iowa and New Jersey while suffering very minor damage.
Retaliation arrived late at night on February 17 when small groups of Japanese bombers flew out of Truk and Formosa. At least five groups between one and three planes attempted to sneak past screening ships to strike fleet carriers. A lone Rikko-type twin engine bomber from the 755th Kōkūtai torpedoed the starboard quarter of Intrepid around 21:00 hours. The attack damaged steering control and killed eleven sailors aboard the carrier. Intrepid was forced to retire to the United States for repairs until August 1944. No other major losses occurred among the American task groups despite repeated attempts by enemy aircraft. These raids demonstrated that some Japanese air power remained active even after the devastating daylight strikes. The limited but damaging counter-attacks highlighted vulnerabilities in the U.S. defensive perimeter surrounding the carriers.
Some 17,000 tons of stored fuel were destroyed by American airstrikes during Operation Hailstone. Shipping losses totaled almost 200,000 tons including several precious fleet oilers with dwindling numbers by early 1944. Vessels sunk at Truk represented almost one-tenth of total Japanese shipping losses between the 1st of November 1943 and the 30th of June 1944. Japan's industrial capability could not replenish such losses in ships or aircraft unlike American rearmament efforts. Admiral Masami Kobayashi faced blame from the Imperial Japanese Navy General Staff and was relieved of command two days later. He went into reserves on the 31st of May 1944 following his removal from active service. Subsequent attacks isolated Truk effectively severing Japanese shipping lanes between home islands and southern resources. The neutralization of Truk paved the way for the invasion of Saipan which placed U.S. bombers within range of Japan itself.
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Common questions
When did Operation Hailstone take place?
Operation Hailstone took place on the 17th of February 1944. Admiral Raymond Spruance ordered Vice Admiral Marc Mitscher's Fast Carrier Task Force to raid Truk Lagoon on this date.
Who commanded American forces during Operation Hailstone?
Admiral Raymond Spruance put himself in tactical command of Task Group 50.9 to engage fleeing Japanese ships directly. His force included four destroyers, heavy cruisers Minneapolis and New Orleans, and battleships Iowa and New Jersey.
What was the outcome for Japanese shipping losses at Truk Lagoon?
Shipping losses totaled almost 200,000 tons including several precious fleet oilers with dwindling numbers by early 1944. Vessels sunk at Truk represented almost one-tenth of total Japanese shipping losses between the 1st of November 1943 and the 30th of June 1944.
Why did Admiral Masami Kobayashi lose his command after Operation Hailstone?
Admiral Masami Kobayashi faced blame from the Imperial Japanese Navy General Staff and was relieved of command two days later. He went into reserves on the 31st of May 1944 following his removal from active service.
How many warplanes were committed to Operation Hailstone by the United States?
Three of four carrier task groups committed over 500 warplanes to the operation. Five fleet carriers and four light carriers formed the core of this massive striking force.