The invasion of Kwajalein in the Marshall Islands finally exposed the Japanese shortfalls in naval and land based aviation to American intelligence officials. Additionally, the increasingly one sided air battles over Rabaul after the invasion of Bougainville proved that the quality of Japanese airpower was in serious decline. To ensure adequate numbers to face the American fighter sweeps over Rabaul, the Japanese were required to “rob Peter to pay Paul” to feed the defense of the South Pacific. Squadrons were transferred from far flung Japanese possessions, including the Gilberts and Marshalls, and sent to Rabaul. The nearly nonexistent Japanese air response to the invasion of Kwajalein convinced Admiral Nimitz to push up the timetable in the Central Pacific, and more specifically the invasion of Eniwetok. However, Eniwetok was within striking distance of the Japanese main naval base in Central Pacific: the Truk Atoll in the Caroline Islands. The “Gibraltar of the Pacific” was essentially a sunken mountain range surrounded by coral reefs and has, by far, the best natural lagoon in the Central Pacific. Its 50 by 30 mile sheltered anchorage has so far in the war allowed the Japanese to strike Pearl Harbor and conduct continuous operations in the South Pacific.

Like Rabaul for Allied planners, Truk was The Lair of the Boogeyman from which All Bad Things Emerged.

Nimitz needed to neutralize Truk. His plan for the Central Pacific involved a future invasion, but the operation to secure the Marshalls meant something had to be done immediately.

By the beginning of 1944, American industry produced enough new aircraft carriers to allow the formation of fast carrier “strike groups”. These strike groups raided Japanese held airfields, anchorages and shipping all throughout the Central and South Pacific. Nimitz formed the largest such strike group so far in the war, Task Force 58 under Vice Admiral Marc Mitscher of five fleet carriers, six light carriers, and seven new fast battleships with accompanying cruisers and destroyers as escorts.

Task Force 58 was a massive force, nearly double the Japanese strength against Pearl Harbor just two years before, but it was still headed for Truk. The idea of willingly sailing aircraft carriers into range of major land based airpower was still alien and unthinkable to most carrier admirals. (The only reason the Japanese did it at Pearl Harbor was because they hadn’t declared war yet. Even at Midway, the main threat was still the island, all the way up until four of their carriers were sunk.) And Truk was the biggest Japanese base outside of Japan. On 15 February when Mitscher announced over the loudspeaker their destination for Operation Hailstone, one of his pilots said, “I nearly jumped overboard.”

However, as early as October 1943, the Japanese recognized they could no longer hold the outer perimeter of the Greater East Asian Co-Prosperity Sphere, and settled on a smaller more easily defensible perimeter to gather strength for a counter attack. They withdrew most of the capital ships from Truk back to the Palaus, so few of the juicy targets remained. The mighty Yamato and Musashi had spent almost 18 months at Truk and had only recently departed. Nevertheless, the withdrawal to the inner perimeter meant that much of the shipping form the outer bases went to Truk first, a major transit point, before heading west. Mitscher’s raid caught the lagoon without capital ships, but filled with arguably more important transport and cargo ships that the Japanese could ill afford to spare.

On the morning of 17 February 1944, Task Force 58 approached Truk behind a storm front and struck the airfields first just as the Japanese did on the morning of the 7th of December 1941. American surprise was complete. Japanese pilots were mostly on shore leave, but the 90 or so Mitsubishi “Zeros” that went up were promptly shot down. By 1944, the Zero was outclassed in almost every category by the new American Hellfighters and Corsairs, and due to fuel and training shortfalls, American pilots had hundreds of more hours in the air than their Japanese counterparts. By the afternoon, any Japanese air response was non-existent, and the Mitscher’s dive and torpedo bombers attacked Truk’s lagoon and shore facilities with impunity. They only had to worry about a few manually controlled anti-aircraft guns and these were quickly dispatched once they revealed their positions.

Unlike Nagumo’s raid at Pearl Harbor, Mitscher didn’t withdraw after two strikes, but launched 13 separate strikes against Truk. Even Mitscher’s boss, Adm Ray Spruance, wanted to get in on the action. He took tactical command of the battleships New Jersey and Iowa and some escorts to chase down fleeing Japanese ships that managed to escape the lagoon. Only darkness ceased Operation Hailstone.

And it was in the darkness that the Japanese managed to strike back: a single torpedo from a “Kate” night bomber penetrated the screen and struck the carrier Intrepid.

For the loss of about 25 planes, most whose pilots were rescued and about 40 personnel, mostly from the Intrepid, Mitscher sunk five cruisers, four destroyers, and almost forty support, transport and cargo ships, including the all-important fleet oilers, and damaged many more. His fliers either shot down or destroyed on the ground almost 250 planes, and over 4500 Japanese personnel were killed, and twice that number wounded, most of whom could not be evacuated.

The destruction of the Truk anchorage convinced Nimitz that it could be bypassed and that an invasion was unnecessary. In the space of just 12 hours, the mightiest Japanese naval base outside of the home islands went from being the focus of all American operations in the Pacific to a tiny and obscure footnote in most Pacific War history books.