Japan didn’t know it at the time, but it had a 6-to-2 aircraft carrier advantage over the U.S. Pacific Fleet as it sailed toward Pearl Harbor and a date with history on Dec. 7, 1941.

The U.S. Navy didn’t do America’s cause in the Pacific any favors either, when it pulled a quarter of its ships over the spring and summer for what was perceived to be a greater need in the Atlantic.

Six Imperial Japanese Navy flattops were involved in the successful air raid on Oahu. Japan didn’t know the exact number of aircraft carriers the U.S. Navy had in the region, but the Naval General Staff estimated four.

The Japanese grouping represented the most powerful carrier task force ever assembled in an era when airplanes launched from ships would revolutionize naval warfare and when the battleship would cease to be the dominant force.

The U.S. Navy, in fact, had just two carriers in the central Pacific: the Lexington and Enterprise. The Saratoga was in San Diego to pick up its air wing on Dec. 7 following dry-dock repairs at Bremerton, Wash.

The Lexington and Enterprise were not in Pearl Harbor, either, which was among the few factors that went in favor of America that fateful day.

“Evidently, Lady Luck, who up to this point had beamed affectionately upon the Japanese, had decided to give the Americans a break,” wrote Gordon W. Prange, Donald M. Goldstein and Katherine V. Dillon in “At Dawn We Slept.”

A “war warning” had been issued Nov. 27 by the Navy Department cautioning not against a Japanese attack on Hawaii, but rather against probable Japanese moves against the Philippines, Thailand, Malaya or possibly Borneo.

The Enterprise sailed from Pearl Harbor on Nov. 28 with three heavy cruisers and nine destroyers to deliver to Wake Island — which was part of the supply line to the Philippines — 12 Wildcat fighters and 13 pilots from Marine Fighter Attack Squadron 211 at Marine Corps Air Station Ewa.

Following the airplane drop-off, the Enterprise was due back at Pearl Harbor on Dec. 6, but a storm slowed the task force — with the “Big E’s” crew complaining they would not make Saturday night in port. At dawn on Dec. 7 the carrier was 215 miles west of Oahu. Some of the carrier’s aircraft were caught up in the Japanese attack and shot down.

The Lexington left Pearl Harbor on Dec. 5, accompanied by three heavy cruisers and five destroyers, and with a similar reinforcement support job to the west. In this case the task force was bound for Midway Atoll with 18 Marine Corps Vought SB2U Vindicator dive bombers aboard.

When word came of the Pearl Harbor attack, the Lexington launched search planes to hunt for the Japanese fleet, and at midmorning headed south to rendezvous with the USS Indianapolis and USS Enterprise task forces and to conduct a search southwest of Oahu before returning to Pearl Harbor on Dec. 18, the Navy said.

The decision had been made in early 1941 that the Atlantic and the threat from Germany would take priority over the Pacific.

Adm. Husband E. Kimmel, commander of the U.S. Pacific Fleet, had lost the aircraft carrier Yorktown, three battleships, four light cruisers and two destroyer squadrons to the Atlantic.

Gen. George C. Marshall, the U.S. Army chief of staff, placed faith in B-17 Flying Fortresses — which never materialized in required numbers — for the long-range defense of Hawaii.

Adm. Isoroku Yamamoto, commander of Japan’s Combined Fleet, expected to eliminate a fifth to a quarter of the U.S. Pacific Fleet with the attack — but the U.S. government had obligingly dispatched that much to the Atlantic, Prange and the others wrote.

Still, Yamamoto could not assume the situation would continue. President Franklin D. Roosevelt could order the ships back. Japan “had evolved a war plan so grandiose, with so much at stake,” that Yamamoto was convinced he could not afford to attack in Southeast Asia — Malaya, the Philippines and Dutch East Indies, Japan’s real goal — without also crippling the U.S. Pacific Fleet, according to “At Dawn We Slept.”