United States Navy in World War II The United States Navy grew rapidly during World War II from 1941 – 45 , and played the central role in the war against Japan , and a major role in the European war against Germany and Italy . The U . S . Navy grew into a formidable force in the years prior to World War II , with battleship production being restarted in 1937 , commencing with the . It was able to add to its fleets during the early years of the war while the US was still neutral , increasing production of vessels both large and small . Though ultimately unsuccessful , Japan attempted to allay this strategic threat with the 1941 surprise attack on Pearl Harbor . Following American entry into the war , the U . S . Navy grew tremendously as the United States was faced with a two - front war on the seas . It achieved notable acclaim in the Pacific Theater , where it was instrumental to the Allies ' successful " island hopping " campaign . The U . S . Navy fought six great battles with the Imperial Japanese Navy ( IJN ) : the Attack on Pearl Harbor , Battle of the Coral Sea , the Battle of Midway , the Battle of the Philippine Sea , the Battle of Leyte Gulf , and the Battle of Okinawa . By 1943 , the Navy ' s size was larger than the combined fleets of all the other combatant nations in World War II . By war ' s end in 1945 , the United States Navy had added hundreds of new ships , including 18 aircraft carriers and 8 battleships , and had over 70 % of the world ' s total numbers and total tonnage of naval vessels of 1 , 000 tons or greater . At its peak , the U . S . Navy was operating 6 , 768 ships on V - J Day in August 1945 , including 28 aircraft carrier s , 23 battleship s , 71 escort carrier s , 72 cruiser s , over 232 submarine s , 377 destroyer s , and thousands of amphibious , supply and auxiliary ships . Doctrine had significantly shifted by the end of the war . The United States Navy had followed in the footsteps of the navies of Britain and Germany which favored concentrated groups of battleships as their main offensive naval weapons . The development of the aircraft carrier and its devastating utilization by the Japanese against the U . S . at Pearl Harbor however shifted U . S . thinking . The Pearl Harbor attack destroyed or took out of action most of the American battleships . This placed much of the burden of retaliating against the Japanese on the small number of aircraft carriers . 1941 – 42 . Iceland . On 16 June 1941 , after negotiation with Churchill , Roosevelt ordered the United States occupation of Iceland to replace the British invasion forces . On 22 June 1941 , the US Navy sent Task Force 19 ( TF 19 ) from Charleston , South Carolina to assemble at Argentia , Newfoundland . TF 19 included 25 warships and the 1st Provisional Marine Brigade of 194 officers and 3714 men from San Diego , California under the command of Brigadier General John Marston . Task Force 19 ( TF 19 ) sailed from Argentia on 1 July . On 7 July , Britain persuaded the Althing to approve an American occupation force under a U . S . - Icelandic defense agreement , and TF 19 anchored off Reykjavík that evening . U . S . Marines commenced landing on 8 July , and disembarkation was completed on 12 July . On 6 August , the U . S . Navy established an air base at Reykjavík with the arrival of Patrol Squadron VP - 73 PBY Catalina s and VP - 74 PBM Mariner s . U . S . Army personnel began arriving in Iceland in August , and the Marines had been transferred to the Pacific by March , 1942 . Up to 40 , 000 U . S . military personnel were stationed on the island , outnumbering adult Icelandic men ( at the time , Iceland had a population of about 120 , 000 . ) The agreement was for the US military to remain until the end of the war ( although the US military presence in Iceland remained through 2006 ) . Pearl Harbor . Pearl Harbor was one of the worst defeats in American history . The U . S . was caught by total surprise and the battle was completely one - sided . Admiral Isoroku Yamamoto , in overall command , argued the only way to win the war was to knock out the main American fleet immediately . His elaborately trained fleet approached within of Hawaii without being detected . Admiral Chuichi Nagumo had tactical command . Over a five hour period his six carriers sent two waves of 350 dive - bombers , torpedo planes and fighters . They destroyed or severely damaged eight battleships , ten smaller warships , and 230 aircraft ; 2 , 400 American soldiers and sailors were killed . Japanese losses were negligible — 29 planes shot down ( several American planes were also shot down by anti - aircraft fire by mistake ) . Commander Minoru Genda , the chief planner of the raid , begged Nagumo to strike again at the shore facilities , oil storage tanks , and submarines , and to hunt down the American carriers that were supposedly nearby . But Nagumo , having just smashed the Americans in one of the greatest victories of naval history , decided not to risk further action . Japanese success was due to courage , good equipment , excellent pilots , total surprise , and above all , a daring and imaginative plan . To even reach Pearl Harbor they had to learn how to refuel at sea ( a technique the US Navy already had worked out ) ; to sink all those ships they used their superb electric torpedoes and perfected shallow - water bombing tactics . Surprise was decisive . While everyone knew that war was imminent , no one at Pearl expected an attack . The commanders had been complacent about routine defensive measures . Even if the defense had been more alert , the surprise and overwhelming power of the Japanese strike probably would have been decisive . But in the broader perspective , the attack was a failure . The lost battleships reflected obsolete doctrine and were not needed ; the lost planes were soon replaced ; the casualty list was short by World War II standards ; perhaps most importantly , the US did not lose its three aircraft carriers . Tokyo ' s calculation that the Americans would lose heart and seek a compromise peace within a few months proved wildly wrong — the " sneak attack " electrified public opinion , committing America with near unanimity to a war to the death against the Japanese Empire . Aftermath . After Pearl Harbor the Imperial Japanese Navy ( IJN ) seemed unstoppable because it outnumbered and outgunned the disorganized Allies — US , Britain , Netherlands , Australia , China . London and Washington both believed in Mahanian doctrine , which stressed the need for a unified fleet . However , in contrast to the cooperation achieved by the armies , the Allied navies failed to combine or even coordinate their activities until mid - 1942 . Tokyo also believed in Mahan , who said command of the seas — achieved by great fleet battles — was the key to sea power . Therefore the IJN kept its main strike force together under Admiral Yamamoto and won a series of stunning victories over the Americans and British in the 90 days after Pearl Harbor . Outgunned at sea , with its big guns lying at the bottom of Pearl Harbor , the American strategy for victory required a slow retreat or holding action against the IJN until the much greater industrial potential of the US could be mobilized to launch a fleet capable of projecting Allied power to the enemy heartland . Guadalcanal . Guadalcanal , fought from August 1942 to February 1943 , was the first major Allied offensive of the war in the Pacific Theater . This campaign saw American air , naval and ground forces ( later augmented by Australians and New Zealanders ) in a six months campaign slowly overwhelm determined Japanese resistance . Guadalcanal was the key to control the Solomon Islands , which both sides saw as strategically essential . Both sides won some battles but both sides were overextended in terms of supply lines . The rival navies fought seven battles , with the two sides dividing the victories . They were : Battle of Savo Island , Battle of the Eastern Solomons , Battle of Cape Esperance , Battle of the Santa Cruz Islands , Naval Battle of Guadalcanal , Battle of Tassafaronga and Battle of Rennell Island . Both sides pulled out its aircraft carriers , as they were too vulnerable to land - based aviation . Midway . The Battle of Midway , together with the Guadlcanal campaign , marked the turning point in the Pacific . Between June 4 – 7 , 1942 , the United States Navy decisively defeated a Japanese naval force that had sought to lure the U . S . carrier fleet into a trap at Midway Atoll . The Japanese fleet lost four aircraft carriers to the U . S . Navy ' s one American carrier and a destroyer . After Midway , and the exhausting attrition of the Solomon Islands campaign , Japan ' s shipbuilding and pilot training programs were unable to keep pace in replacing their losses while the U . S . steadily increased its output in both areas . Military historian John Keegan called the Battle of Midway " the most stunning and decisive blow in the history of naval warfare . " 1943 . In preparation of the recapture of the Philippines , the Allies started the Gilbert and Marshall Islands campaign to retake the Gilbert and Marshall Islands from the Japanese in summer 1943 . Enormous effort went into recruiting and training sailors and Marines , and building warships , warplanes and support ships in preparation for a thrust across the Pacific , and to support Army operations in the Southwest Pacific , as well as in Europe and North Africa . 1944 . The Navy continued its long movement west across the Pacific , seizing one island base after another . Not every Japanese stronghold had to be captured ; some , like the big bases at Truk , Rabaul and Formosa were neutralized by air attack and then simply leapfrogged . The ultimate goal was to get close to Japan itself , then launch massive strategic air attacks and finally an invasion . The US Navy did not seek out the Japanese fleet for a decisive battle , as Mahanian doctrine would suggest ; the enemy had to attack to stop the inexorable advance . Battle of the Philippine Sea . The climax of the carrier war came at the Battle of the Philippine Sea . Taking control of islands that could support airfields within B - 29 range of Tokyo was the objective . 535 ships began landing 128 , 000 Army and Marine invaders on June 15 , 1944 in the Mariana and Palau Islands . The achievement in planning such a complex logistical operation in just ninety days , and staging it from Pearl Harbor was indicative of American logistic superiority . ( The previous week an even bigger landing force hit the beaches of Normandy — by 1944 the Allies had resources to spare . ) The Japanese launched an ill - coordinated attack on the larger American fleet ; its planes operated at extreme ranges and could not keep together , allowing them to be easily shot down in what Americans jokingly called the " Great Marianas Turkey Shoot . " Japan had now lost all its offensive capabilities , and the U . S . had control of Guam , Saipan and Tinian islands that provided air bases within range of B - 29 bombers targeted at Japan ' s home islands . It was entirely an air battle , in which Americans had all the technological advantages . It was the largest naval battle in history , to day , surpassed only by the Battle of Leyte Gulf in October 1944 . Japanese strategy . The American 5th Fleet covering the landing comprised 15 big carriers and 956 planes , plus 28 battleships and cruisers , and 69 destroyers . Tokyo sent Vice Admiral Jisaburo Ozawa with nine - tenths of Japan ' s fighting fleet — it was about half the size of the American force , and included nine carriers with 473 planes , 18 battleships and cruisers , and 28 destroyers . Ozawa ' s pilots boasted of their fiery determination , but they had only a fourth as much training and experience as the Americans . They were outnumbered 2 - 1 and used inferior equipment . Ozawa had anti - aircraft guns but lacked proximity fuzes and good radar . Ozawa gambled on surprise , luck and a trick strategy , but his battle plan was so complex and so dependent on good communications that it quickly broke down . His planes carried more gasoline because they were not weighted down with protective armor ; they could attack at , and could search a radius of 560 miles . The heavier American Hellcats could only attack to , and only search to 325 . Ozawa ' s plan therefore was to use his advantage in range by positioning his fleet out , forcing the Americans to search over of ocean just to find him . The Japanese ships would stay beyond American range , but their planes would have enough range to strike the American fleet . They would hit the carriers , land at Guam to refuel , then hit the Americans en route back to their carriers . Ozawa counted heavily on the 500 or so ground - based planes that had been flown ahead to Guam and other islands in the area . 1945 . Okinawa . Okinawa was the last great battle of the entire war . The goal was to make the island into a staging area for the invasion of Japan scheduled for fall 1945 . It was just 350 miles ( 550 km ) south of the Japanese home islands . Marines and soldiers landed on 1 April 1945 , to begin an 82 - day campaign which became the largest land - sea - air battle in history and was noted for the ferocity of the fighting and the high civilian casualties with over 150 , 000 Okinawans losing their lives . Japanese kamikaze pilots enacted the largest loss of ships in U . S . naval history with the sinking of 38 and the damaging of another 368 . Total U . S . casualties were over 12 , 500 dead and 38 , 000 wounded , while the Japanese lost over 110 , 000 men . The fierce combat and high American losses led the Navy to oppose an invasion of the main islands . An alternative strategy was chosen : using the atomic bomb to induce surrender . Naval technology . Technology and industrial power proved decisive . Japan failed to exploit its early successes before the immense potential power of the Allies could be brought to bear . In 1941 the Japanese Zero fighter had a longer range and better performance than rival American warplanes , and the pilots had more experience in the air . But Japan never improved the Zero and by 1944 the Allied navies were far ahead of Japan in both quantity and quality , and ahead of Germany in quantity and in putting advanced technology to practical use . High tech innovations arrived with dizzying rapidity . Entirely new weapons systems were invented — like the landing ships , such as the 3 , 000 ton LST ( " Landing Ship Tank " ) that carried 25 tanks thousands of miles and landed them right on the assault beaches . Furthermore , older weapons systems were constantly upgraded and improved . Obsolescent airplanes , for example , received more powerful engines and more sensitive radar sets . One impediment to progress was that admirals who had grown up with great battleships and fast cruisers had a hard time adjusting their war - fighting doctrines to incorporate the capability and flexibility of the rapidly evolving new weapons systems . Ships . The ships of the American and Japanese forces were closely matched at the beginning of the war . By 1943 the American qualitative edge was winning battles ; by 1944 the American quantitative advantage made the Japanese position hopeless . The German Navy , distrusting its Japanese ally , ignored Hitler ' s orders to cooperate and failed to share its expertise in radar and radio . Thus the Imperial Navy was further handicapped in the technological race with the Allies ( who did cooperate with each other ) . The United States economic base was ten times larger than Japan ' s , and its technological capabilities also significantly greater , and it mobilized engineering skills much more effectively than Japan , so that technological advances came faster and were applied more effectively to weapons . Above all , American admirals adjusted their doctrines of naval warfare to exploit the advantages . The quality and performance of the warships of Japan were initially comparable to that of the US . The Americans were supremely , and perhaps overly , confident in 1941 . Pacific commander Admiral Chester W . Nimitz boasted he could beat a bigger fleet because of " . . . our superior personnel in resourcefulness and initiative , and the undoubted superiority of much of our equipment . " As Willmott notes , it was a dangerous and ill - founded assumption . Battleships . The American battleships before Pearl Harbor could fire salvos of nine 2 , 100 pound armor - piercing shells every minute to a range of 35 , 000 yards ( 19 miles ) . No ship except another battleship had the thick armor that could withstand that kind of firepower . When intelligence reported that Japan had secretly built even more powerful battleships , Washington responded with four " Iowa " class battleships ( two of which were used a half - century later in the Gulf War . ) The " big - gun " admirals on both sides dreamed of a great shootout at twenty - mile ( 32 km ) range , in which carrier planes would be used only for spotting the mighty guns . Their doctrine was utterly out of date . A plane like the Grumman TBF Avenger could drop a 2 , 000 pound bomb on a battleship at a range of hundreds of miles . An aircraft carrier cost less , required about the same number of personnel , was just as fast , and could easily sink a battleship . During the war the battleships found new missions : they were platforms holding all together dozens of anti - aircraft guns and 8 or 9 14 " or 16 " long - range guns used to blast land targets before amphibious landings . Their smaller 5 " guns , and the 4 , 800 3 " to 8 " guns on cruisers and destroyers also proved effective at bombarding landing zones . After a short bombardment of Tarawa island in November 1943 , Marines discovered that the Japanese defenders were surviving in underground shelters . It then became routine doctrine to thoroughly work over beaches with thousands of high explosive and armor piercing shells . The bombardment would destroy some fixed emplacements and kill some troops . More important , it severed communication lines , stunned and demoralized the defenders , and gave the landing parties fresh confidence . After the landing , naval gunfire directed by ground observers would target any enemy pillboxes that were still operational . The sinking of the battleships at Pearl Harbor proved a blessing in deep disguise , for after they were resurrected and assigned their new mission they performed well . ( Absent Pearl Harbor , big - gun admirals like Raymond Spruance might have followed prewar doctrine and sought a surface battle in which the Japanese would have been very hard to defeat . ) Naval aviation . In World War I the Navy explored aviation , both land - based and carrier based . However the Navy nearly abolished aviation in 1919 when Admiral William S . Benson , the reactionary Chief of Naval Operations , could not " conceive of any use the fleet will ever have for aviation " , and he secretly tried to abolish the Navy ' s Aviation Division . Assistant Secretary of the Navy Franklin D . Roosevelt reversed the decision because he believed aviation might someday be " the principal factor " at sea with missions to bomb enemy warships , scout enemy fleets , map mine fields , and escort convoys . Grudgingly allowing it a minor mission , the Navy slowly built up its aviation . In 1929 it had one carrier ( ) , 500 pilots and 900 planes ; by 1937 it had 5 carriers ( the , , " Ranger " , and ) , 2000 pilots and 1000 much better planes . With Roosevelt now in the White House , the tempo soon quickened . One of the main relief agencies , the PWA , made building warships a priority . In 1941 the U . S . Navy with 8 carriers , 4 , 500 pilots and 3 , 400 planes had more airpower than the Japanese Navy .