World War II: Operation Hailstone

Japanese ammunition ship Aikoku Maru explodes during Operation Hailstone. Photograph Courtesy of the US Navy

Operation Hailstone - Conflict & Dates:

Operation Hailstone was conducted February 17-18, 1944, during World War II (1939-1945).

Operation Hailstone - Fleets & Commanders:

United States


  • Vice Admiral Masami Kobayashi

  • 5 cruisers, 8 destroyers, 5 other warships, 50 merchant vessels

Operation Hailstone - Background:

Assuming control of the Caroline Islands during World War I, Japan received a League of Nations mandate over the chain in 1919.

  During the next two decades, the Japanese ignored the restrictions of the mandate and actively sought to colonize and fortify the islands in Truk Lagoon.  By the start of World War II, the Imperial Japanese Navy had constructed four airstrips, a variety of defenses, as well as facilities for supporting the Combined Fleet.  Dubbed the "Gibraltar of the Pacific", Truk served as Japan's largest naval base outside of the home islands and fulfilled a role similar to Pearl Harbor for the US Navy.  As the war in the Southwest Pacific raged in August 1942, the commander-in-chief of the Combined Fleet, Admiral Isoroku Yamamoto, established his headquarters in the lagoon aboard the battleship Yamato.  

Following Allied victories at Guadalcanal in the Solomons and Tarawa in the Gilberts, the commander-in-chief of the US Pacific Fleet, Admiral Chester W. Nimitz, began planning for a campaign in the Marshalls early in 1944.

  Attacking Kwajalein on January 31, Allied troops captured the island three days later.  Worried that the loss of Kwajalein, a thousand miles to the east, threatened Truk, Admiral Mineichi Koga, who had assumed leadership of the fleet after Yamamoto's death the previous year, ordered his carriers and other heavy warships to withdraw to Palau on February 10.


Operation Hailstone - Allied Plans:

With the conclusion of operations against Kwajalein, Nimitz and Admiral Raymond A. Spruance turned their attention to nearby Eniwetok.  Concerned about potential interference from Truk, Spruance directed Rear Admiral Marc A. Mitscher to take Task Force 58 (Fast Carrier Task Force) and mount a series of strikes against the lagoon.  Comprised of the fleet carriers USS Enterprise (CV-6), USS Essex (CV-9), USS Yorktown (CV-10), USS Intrepid (CV-11), and USS Bunker Hill (CV-17) as well as the light carriers USS  (CVL-24), USS Cowpens (CVL-25), USS Monterey (CVL-26), and USS Cabot (CVL-28), TF 58 possessed over 500 aircraft. 

Supporting the carrier force were seven battleships as well as numerous cruisers and destroyers.  Approaching Truk in mid-February, Mitscher advanced some of his surface forces to block escape routes from the lagoon.  As TF 58 moved into position, the submarine USS Skate scored a success when it sunk the light cruiser Agano approximately 170 miles north of Truk on February 15.  One of the cruiser's escorts, the destroyer Oite, rescued survivors and turned back toward the lagoon.

Operation Hailstone - Mitscher Strikes:         

In position before dawn on February 17, TF 58 began launching an initial wave of 72 F6F Hellcat fighters.

  Led by Lieutenant Commander William Kane from Enterprise, this force approached Truk and engaged patrolling Japanese fighters.  Sweeping these aside, Kane's aircraft commenced strafing the enemy airstrips as additional aircraft from TF 58 arrived.  Reaching the anchorage, SBD Dauntless dive bombers and TBF Avenger torpedo bombers found a number of light warships and a multitude of merchant shipping below.  Beginning their attacks, the American aircraft inflicted widespread devastation across the anchorage and on the adjacent facilities. 

Attacks continued through the day as waves of American aircraft continued to strike at the Japanese.  To the north of Truk, a small convoy led by the light cruiser Katori and consisting of the destroyers Maikaze and Nowaki, auxiliary cruiser Akagi Maru, and the minesweeper Shonan Maru No. 15 was spotted.

  While aircraft sunk Akagi Maru, the remaining ships later encountered Rear Admiral Robert C. Giffen's Task Group 50.9 which was centered on the battleships USS Iowa (BB-61) and USS New Jersey (BB-62).  Bringing the Japanese under fire, they sank both Katori and Maikaze.

That evening, Mitscher ordered radar-equipped Avengers to continue raids against the lagoon.  During the night, TF 58 came under attack from Japanese aircraft which resulted in a torpedo hit on Intrepid.  Departing TF 58 a short time later, the carrier was out of action for four months.  At dawn on February 18, Mitscher resumed large-scale raids against Truk.  Reaching the lagoon, American pilots increasing found it difficult to locate new targets.  Concluding the mission later in the day, Mitscher and TF 58 departed the area. 

Operation Hailstone - Aftermath:

Successful in covering the landings on Eniwetok, Operation Hailstone resulted in the Japanese loss of 3 light cruisers, 4 destroyers, 8 smaller warships, 32 merchant vessels, and approximately 275 aircraft.  American casualties numbered 40 killed and 25 aircraft.  Mitscher's strikes on Truk, as well as a follow-up raid in April, effectively eliminated the lagoon's effectiveness as a base for the Japanese.  Increasingly isolated by American thrusts through the Marianas and Palaus, Truk's garrison faced a variety of shortages for the remainder of the war.   Facing starvation, the last Japanese forces at Truk surrendered in August 1945.

Selected Sources