1

Meet the U.S. Navy Cruiser That Carried the Atom Bomb (And Then Sank)

November 15, 2019 Topic: Security Blog Brand: The Buzz Tags: MilitaryTechnologyWeaponsWarBombWorld War II

Meet the U.S. Navy Cruiser That Carried the Atom Bomb (And Then Sank)

The USS Indianapolis transported atomic devices and then sank in the closing days of World War II.

Key Point: Later retold in the movie blockbuster Jaws, the story of the USS Indianopolis is an important capstone to the Second World War. 

There was tight security and feverish activity on the dock at the Hunters Point Navy Shipyard in San Francisco Bay around 3 am on Monday, July 16, 1945.

Two U.S. Army trucks unloaded a precious cargo—a large crate and a two-foot-long metal cylinder containing a uranium projectile and components for the “Little Boy” bomb, destined to be dropped on the Japanese city of Hiroshima and usher in the atomic age.

Moored at the dock and making ready to get underway was the fast, heavy cruiser USS Indianapolis (CA-35), commanded by 46-year-old Captain Charles B. McVay. As soon as a big gantry crane quickly lowered the cargo aboard the ship, the crate was secured to the deck and surrounded by a U.S. Marine guard, and the cylinder was placed in the flag lieutenant’s cabin.

Rear Admiral William R. Purnell, the naval member of the Manhattan Project’s Military Policy Committee, told McVay that if the ship ran into trouble the cylinder was to be saved at all costs. The ship would be carefully tracked during its voyage, and if anything happened to her, it would be known within hours.

It was a unique, top-secret assignment for the 13-year-old Indianapolis. Rushed to completion and commissioned on November 15, 1932, she and her sister ship, the USS Portland, were modifications of the Northampton-class cruisers. They were critically top heavy with new electronics, light antiaircraft weaponry, and fire control gear.

With a complement of 1,196 officers and sailors, the Indianapolis displaced 9,800 tons, was 610 feet long, and had a top speed of 32.5 knots. Her armament included nine 8-inch guns, eight 5-inch dual-purpose guns, and two 3-pounder guns. Though a “treaty cruiser” with some design deficiencies like others of the Northampton class, the Indianapolis was a proud member of the U.S. Fleet. She boasted a handsome teak quarterdeck before being stripped for war and had an enviable reputation for sharp ceremonies and honors performed by her Marine Corps detachment.

As a lifelong private sailor, former Assistant Secretary of the Navy, and fervent advocate of sea power, President Franklin D. Roosevelt held a special affinity for the Indianapolis. He watched seagoing maneuvers from her deck in May 1934 and sailed aboard her when he undertook his unprecedented “Good Neighbor Policy” cruise to Latin America in late November 1936.

At 8 on the morning of July 16, 1945, the Indianapolis cast off, bound for the island of Tinian in the distant Marianas group. She steamed under the Golden Gate Bridge half an hour later and headed westward across the Pacific Ocean. Recently patched up at Mare Island, California, after being severely damaged by a Japanese kamikaze plane on March 31, 1945, during the Okinawa invasion, the cruiser was a veteran of more than three years of fleet duty. She had been with the Pacific Fleet from the time of the Pearl Harbor raid on December 7, 1941.

When the cruiser USS Indianapolis was sunk in 1945, the warship was one of the best known in the U.S. Navy and a favorite of President Franklin D. Roosevelt, who visited on several occasions and used the cruiser for some diplomatic travel.

After taking part in early 1942 raids, she saw action in almost every major amphibious invasion in the Central Pacific and lent fire support in the Aleutians, Gilberts, Marshalls, Kwajalein, Eniwetok, Saipan, Guam, Palau, and Iwo Jima operations. The Indianapolis also served as the principal flagship of Vice Admiral Raymond A. Spruance when he commanded the Fifth Fleet.

Captain McVay, who ran a tight ship and was generally regarded as heading for higher flag rank, pushed his engine room crew to maintain top speed during the long voyage to the destination—the Twentieth Air Force’s Boeing B-29 Superfortress heavy bomber base on Tinian, three miles south of Saipan.

The cruiser reached the volcanic, 50-square-mile island shortly after daybreak on Thursday, July 26. Because Tinian did not have an adequate harbor, the Indianapolis dropped anchor 1,000 yards offshore. As small craft swarmed around the cruiser, high-ranking officers of all services climbed aboard to watch the unloading of the top secret cargo, the heart of the world’s first practical atomic bomb. A crane lifted the crate and cylinder into a waiting LCT (landing craft, tank), which promptly headed for shore. The cruiser had completed her unique mission, and McVay’s grave responsibility was over.

The cruiser then weighed anchor and steamed to Guam, the southernmost island in the Marianas, where McVay was briefed and given new orders. The Indianapolis was to head for Leyte Gulf in the Philippines for two weeks of training exercises before rejoining the fleet and preparing for the Allied invasion of the Japanese home islands. Unescorted, the cruiser departed from Guam on July 28 and proceeded westward.

McVay and his crew were unaware of the dire perils that lay ahead. “There was no mention made of any untoward incident in the area through which I was to pass,” he reported later. “I definitely got the idea … that it was a routine voyage.” A lieutenant and an ensign aboard the cruiser charted a direct, straight-line route at 15.7 knots estimated to get the ship into Leyte on July 31.

Surface and air units of the Imperial Japanese Navy had been rendered virtually impotent by late that month. In strikes against airfields, the naval base at Kure, and shipping in the Inland Sea, the powerful Task Force 38 of Admiral William F. “Bull” Halsey’s U.S. Third Fleet sank or badly damaged numerous enemy vessels, including the battleships Haruna, Ise, and Hyuga; the carriers Amagi, Katsuragi, and Ryuho; the heavy cruiser Tone; and the cruisers Aoba and Oyoda.

The Americans had written off the Japanese fleet as a threat in rear areas, but it was not quite finished because a few of its submarines were still at large. A final offensive by six diesel-powered I-boats, each carrying six kaiten one-man midget submarines (human torpedoes) as well as conventional Long Lance torpedoes, was underway in the Western Pacific.

Early that month, U.S. intelligence experts had decoded Japanese messages and confirmed the presence of four enemy submarines in the main shipping lane to Leyte. On July 24, while shepherding a convoy from Okinawa to Leyte, the destroyer escort USS Underhill was crippled off Luzon by a kaiten from I-53 and then scuttled by submarine chasers. The death toll was 112 officers and men. But an Ultra intelligence intercept of a message from Lt. Cmdr. Mochitsura Hashimoto claiming that his I-58 had sunk an American battleship was dismissed as the usual Japanese exaggeration.

The Indianapolis sailed on across the Philippine Sea, but a series of errors and oversights was sealing her fate. She had no underwater detection equipment and was dependent on radar and eyesight to detect a submarine. Routing officers, meanwhile, had told McVay that he would not need an escort. The cruiser was on her own, and her whereabouts would be unknown for several critical days.

A headquarters radio message to the battleship USS Idaho in the Gulf of Leyte, reporting that the Indianapolis was on her way there, was incorrectly decoded and discarded. Next, a Navy radio relay station on Okinawa somehow lost a routing message to Leyte saying that the cruiser had left Guam. Leyte was unaware that the ship was coming.

Seven hours after the cruiser left Guam, the merchant ship SS Wild Hunter dispatched an urgent message from farther along the cruiser’s planned course, reporting that an enemy periscope had been sighted. The destroyer escort USS Albert Harris and reconnaissance planes investigated but reported losing contact with the submarine.

Steaming to an area northeast of Leyte, the Indianapolis zigzagged to make tracking by enemy forces more difficult, although the maneuver was not required in presumably safe waters. Standard fleet instructions required ships to zigzag only when the visibility was good. Captain McVay’s routing orders directed him to zigzag “at discretion,” which he did by day. The cruiser had no lifeboats and only a few life rafts, but the end of the Pacific War was in sight. The Japanese Navy was no longer seen as a threat, and there was no reason to believe that the voyage to Leyte was anything but a routine assignment.

At twilight on Sunday, July 29, the visibility worsened under cloudy skies and the sea became choppy, so Captain McVay ordered a halt to the zigzagging. The ship resumed a straight, steady course. At 11 pm, after going to the bridge to check on the night watch, he went down to his cabin to sleep.

The Indianapolis was not “buttoned up” above the second deck. Like the Navy’s other aging heavy cruisers, she had no air conditioning to make sleep possible for the crew in tropical waters, so the skipper allowed all ventilation ducts and most bulkheads to remain open. The entire main deck, the doors on the second deck, and the hatches to living spaces below were all open.