On 7 December 1941,
Indianapolis, leading Task Force 3, (
Indianapolis and destroyer-minesweepers , , and from MineDiv 6, and and from MineDiv 5) was conducting a mock bombardment at
Johnston Atoll during the
Japanese attack on Pearl Harbor.
Indianapolis was absorbed into Task Force 12 and searched for the
Japanese aircraft carriers responsible for the attack, though the force did not locate them. She returned to
Pearl Harbor on 13 December and joined
Task Force 11.
New Guinea campaign With the task force, she steamed to the
South Pacific, to south of
Rabaul,
New Britain, escorting the
aircraft carrier . Late in the afternoon of 20 February 1942, the American ships were attacked by 18 Japanese aircraft. Of these, 16 were shot down by aircraft from
Lexington and the other two were destroyed by anti-aircraft fire from the ships. On 10 March, the task force, reinforced by another force centered on the carrier , attacked
Lae and
Salamaua, New Guinea, where the Japanese were marshaling
amphibious forces. Attacking from the south through the
Owen Stanley mountain range, the US air forces surprised and inflicted heavy damage on Japanese warships and transports, losing few aircraft.
Indianapolis returned to the
Mare Island Naval Shipyard for a refit before escorting a convoy to Australia.
Aleutian Islands campaign Indianapolis then headed for the North Pacific to support American units in the
Battle of the Aleutian Islands. On 7 August,
Indianapolis and the task force attacked
Kiska Island, a Japanese staging area. Although fog hindered observation,
Indianapolis and other ships fired their main guns into the bay.
Floatplanes from the cruisers reported Japanese ships sunk in the harbor and damage to shore installations. After 15 minutes, Japanese
shore batteries returned fire before being destroyed by the ships' main guns. Japanese submarines approaching the force were
depth-charged by American
destroyers and Japanese seaplanes made an ineffective bombing attack. In spite of a lack of information on the Japanese forces, the operation was considered a success. US forces later occupied
Adak Island, providing a naval base farther from
Dutch Harbor on
Unalaska Island.
1943 operations In January 1943,
Indianapolis supported a landing and occupation on
Amchitka, part of an
Allied island hopping strategy in the
Aleutian Islands. On the evening of 19 February,
Indianapolis led two destroyers on a patrol southwest of
Attu Island, searching for Japanese ships trying to reinforce Kiska and Attu. She intercepted the Japanese
cargo ship,
Akagane Maru laden with troops, munitions, and supplies. The cargo ship tried to reply to the radio challenge but was shelled by
Indianapolis.
Akagane Maru exploded and sank with all hands. Through mid-1943,
Indianapolis remained near the Aleutian Islands, escorting American convoys and providing shore bombardments supporting amphibious assaults. In May, the Allies captured Attu, then turned on Kiska, thought to be the final Japanese holdout in the Aleutians. Allied landings there began on 15 August, but the Japanese had already abandoned the Aleutian Islands, unbeknownst to the Allies. After refitting at Mare Island,
Indianapolis moved to Hawaii as flagship of
Vice Admiral Raymond A. Spruance, commanding the
5th Fleet. She sortied from Pearl Harbor on 10 November, with the main body of the Southern Attack Force for
Operation Galvanic, the invasion of the
Gilbert Islands. On 19 November,
Indianapolis bombarded
Tarawa Atoll, and next day pounded
Makin (see
Battle of Makin). The ship then returned to Tarawa as fire-support for the landings. Her guns shot down an enemy plane and shelled enemy strongpoints as landing parties fought Japanese defenders in the
Battle of Tarawa. She continued this role until the island was secure three days later. The conquest of the
Marshall Islands followed victory in the Gilberts.
Indianapolis was again 5th Fleet flagship.
1944 pattern The cruiser met other ships of her task force at Tarawa, and on
D-Day minus 1, 31 January 1944, she was one of the cruisers that bombarded the islands of
Kwajalein Atoll. The shelling continued on D-Day, with
Indianapolis suppressing two enemy shore batteries. Next day, she destroyed a blockhouse and other shore installations and supported advancing troops with a
creeping barrage. The ship entered Kwajalein Lagoon, on 4 February, and remained until resistance disappeared (see
Battle of Kwajalein). In March and April,
Indianapolis, still flagship of the 5th Fleet, attacked the
Western Carolines. Carrier planes at the
Palau Islands on 30–31 March, sank three destroyers, 17 freighters, five
oilers and damaged 17 other ships. Airfields were bombed and surrounding water
mined.
Yap and
Ulithi were struck on 31 March, and
Woleai on 1 April. Japanese planes attacked but were driven off without damaging the American ships.
Indianapolis shot down her second plane, a torpedo bomber, and the Japanese lost 160 planes, including 46 on the ground. These attacks prevented Japanese forces stationed in the Carolines from interfering with the US landings on
New Guinea. In June, the 5th Fleet was busy with the assault on the
Mariana Islands. Raids on
Saipan began with carrier-based planes on 11 June, followed by surface bombardment, in which
Indianapolis had a major role, from 13 June (see
Battle of Saipan). On D-Day, 15 June, Admiral Spruance heard that
battleships, carriers, cruisers, and destroyers were headed south to relieve threatened garrisons in the Marianas. Since amphibious operations at Saipan had to be protected, Spruance could not withdraw too far. Consequently, a fast carrier force was sent to meet this threat while another force attacked Japanese air bases on
Iwo Jima and
Chichi Jima, in the
Bonin and
Volcano Islands, bases for potential enemy air attacks. A combined US fleet fought the Japanese on 19 June in the
Battle of the Philippine Sea. Japanese carrier planes, which planned to use the airfields of
Guam and
Tinian to refuel and rearm, were met by carrier planes and the guns of the Allied escorting ships. That day, the U.S. Navy destroyed a reported 426 Japanese planes while losing 29.
Indianapolis shot down one torpedo plane. This day of aerial combat became known as the "Great Marianas Turkey Shoot". With Japanese air opposition wiped out, the US carrier planes sank , two destroyers, and one
tanker and damaged others. Two other carriers, and , were sunk by submarines.
Indianapolis returned to Saipan on 23 June to resume fire support and six days later moved to Tinian to attack shore installations (see
Battle of Tinian). Meanwhile, Guam had been taken, and
Indianapolis became the first ship to enter
Apra Harbor since early in the war. The ship operated in the Marianas for the next few weeks, then moved to the Western Carolines, where further landings were planned. From 12 to 29 September, she bombarded
Peleliu, in the
Palau Group, before and after the landings (see
Battle of Peleliu). She then sailed to
Manus Island, in the
Admiralty Islands, where she operated for 10 days before returning to the Mare Island Naval Shipyard in California for refitting.
1945 Overhauled,
Indianapolis joined Vice Admiral
Marc A. Mitscher's fast carrier task force on 14 February 1945. Two days later, the task force launched an attack on
Tokyo to cover the landings on Iwo Jima, scheduled for 19 February. This was the first carrier attack on mainland Japan since the
Doolittle Raid. The mission was to destroy Japanese air facilities and other installations in the
Home Islands. The fleet achieved complete tactical surprise by approaching the Japanese coast under cover of bad weather. The attacks were pressed home for two days. The U.S. Navy lost 49 carrier planes while claiming 499 enemy planes, a 10-to-1 kill/loss ratio. The task force also sank a carrier, nine coastal ships, a destroyer, two
destroyer escorts, and a cargo ship. They destroyed hangars, shops, aircraft installations, factories, and other industrial targets. Immediately after the strikes, the task force raced to the Bonin Islands to support the
landings on Iwo Jima. The ship remained there until 1 March, protecting the invasion ships and bombarding targets in support of the landings.
Indianapolis returned to VADM Mitscher's task force in time to strike Tokyo, again on 25 February, and
Hachijō, off the southern coast of
Honshū, the following day. Although weather was extremely bad, the American force destroyed 158 planes and sank five small ships while pounding ground installations and destroying trains. The next target for the US forces was
Okinawa, in the
Ryukyu Islands, which were in range of aircraft from the Japanese mainland. The fast carrier force was tasked with attacking airfields in southern Japan until they were incapable of launching effective airborne opposition to the impending invasion. The fast carrier force departed for Japan from Ulithi on 14 March. On 18 March, she launched an attack from a position southeast of the island of
Kyūshū. The attack targeted airfields on Kyūshū, as well as ships of the Japanese fleet in the harbors of
Kobe and
Kure, on southern Honshū. The Japanese located the American task force on 21 March, sending 48 planes to attack the ships. Twenty-four
fighters from the task force intercepted and shot down all the Japanese aircraft.
Indianapolis was assigned to
Task Force 54 (TF 54) for the
invasion of Okinawa. When TF 54 began pre-invasion bombardment of Okinawa on 24 March,
Indianapolis spent seven days pouring 8-inch shells into the beach defenses. During this time, enemy aircraft repeatedly attacked the American ships.
Indianapolis shot down six planes and damaged two others. On 31 March, the day before the
Tenth Army (combined U.S. Army and U.S. Marine Corps) started its assault landings, the
Indianapolis lookouts spotted a Japanese
Nakajima Ki-43 "Oscar" fighter as it emerged from the morning twilight and dived vertically towards the bridge. The ship's 20 mm guns opened fire, but within 15 seconds the plane was over the ship. Tracers converged on it, causing it to swerve, but the pilot managed to release his bomb from a height of , then crashed his plane into the sea near the
port stern. The bomb plummeted through the deck, into the crew's
mess hall, down through the berthing compartment, and through the fuel tanks before crashing through the keel and exploding in the water underneath. The concussion blew two gaping holes in the keel which flooded nearby compartments, killing nine crewmen. The ship's bulkheads prevented any progressive flooding.
Indianapolis, settling slightly by the stern and listing to port, steamed to a salvage ship for emergency repairs. Here, inspection revealed that her propeller shafts were damaged, her fuel tanks ruptured, and her water-distilling equipment ruined.
Indianapolis then steamed under her own power to the Mare Island Naval Shipyard for repairs.
Transporting the atomic bomb atomic bomb (L-11) being assembled at Tinian a few days after its arrival aboard the Indianapolis'' After major repairs and an overhaul,
Indianapolis received orders to undertake a top-secret mission: transporting a "critical shipment" of material for the first
atomic bomb to
Tinian Island. In its hold was loaded the complete non-nuclear parts for a
Little Boy gun-type atomic bomb unit (L-11) and several hundred pounds of scientific instruments and tools. Also on board was the bomb's
enriched uranium "projectile", in the form of discs, which were kept inside a lead-lined steel container that was bolted and chained to the floor of Captain
McVay's quarters for the duration of the journey. Two representatives of the
Manhattan Project, Major
Robert R. Furman and Dr. James F. Nolan, accompanied them on the journey incognito. Nolan, the Chief Medical Officer for
Project Y, was there to monitor the uranium's radioactivity. Nolan was frequently
seasick on the journey, which he used as an excuse to surreptitiously monitor the container. The
Fat Man atomic bomb, used against Nagasaki, was transported by air to Tinian. Other equipment necessary for the atomic bomb mission, including "spare" non-nuclear assemblies, had been previously sent to Tinian on other surface ships. Ships were the preferred method for sending critical materials, when time allowed for it, because the risk of loss was considered smaller than going by air. While not particularly radioactive by itself, the amount of enriched uranium in the shipment was large enough to pose a
criticality risk under certain circumstances, such as being submerged in water (which acts as a
neutron moderator, decreasing the
critical mass).
Indianapolis departed San Francisco's
Hunters Point Naval Shipyard on 16 July 1945, within hours of the
Trinity test in New Mexico. She set a speed record of hours from San Francisco to Pearl Harbor, an average speed of . Arriving at Pearl Harbor on 19 July, she raced on unaccompanied, delivering the atomic bomb components to Tinian on 26 July. On the same day that
Indianapolis offloaded its cargo at Tinian, the remaining of enriched uranium used for the "target" piece of the bomb was divided into three pieces and sent on three different
C-54 cargo planes from
Albuquerque, New Mexico. By 29 July, all three had arrived at Tinian and the next day the assembly of the L-11 atomic bomb unit began. ==Sinking==