Operation `` Hailstone '' ( ) , lit .

Prior to Operation `` Hailstone '' , the IJN had used Using Truk as an anchorage for its large Combined Fleet .

As a result , the Japanese Navy had to relocate Military_operation the Combined Fleet 's forward base to the Palau Islands , and eventually to Indonesia , and the Fleet had begun Process_start clearing Emptying its major warships out of Truk before the `` Hailstone '' attack Attack struck .

Nevertheless , the `` Hailstone '' attack Attack on Truk caught Hold a good number of Japanese auxiliary ships and cargo ships in the harbor , as well as some warships .

Between the air attacks and surface ship attacks over the two days of Operation `` Hailstone '' , the worst blow Motion against the Japanese was about 250 warplanes destroyed Destroying , with the concurrent irreplaceable loss Earnings_and_losses of experienced pilots .