Oahu was an impregnable fortress.

Japan wouldn’t dare attack the United States, a first-rate nation, and its Pacific Fleet in Hawaii. Possibly elsewhere, such as in the Philippines, but certainly not Hawaii.

That was the American mindset — until just before 8 a.m. Dec. 7, 1941.

From the lowest-ranking American defenders who fought back — some still in their teens, and some firing with .45-caliber pistols and Springfield bolt-action rifles — to the Pacific Fleet commander, Adm. Husband E. Kimmel, the Japanese air and submarine attack was a stunning surprise that caught U.S. forces flat-footed.

On the battleship USS Nevada, the band literally played on as bombs fell, so confused were crew members initially as to what was going on.

Kimmel, in his Pearl Harbor headquarters, was surveying the destruction befalling his fleet, and the death that accompanied it, when a bullet crashed through the window and bounced off his chest. Examining it, he remarked, “It would have been merciful had it killed me.”

In the attacks that lasted just over two hours, 2,390 American service members and Oahu civilians were killed; 21 ships of the Pacific Fleet, including eight battleships, were sunk or damaged; and 164 aircraft were destroyed.

Fifty-six Japanese aviators and up to nine midget submarine crew members died.

Seventy-five years later Pearl Harbor continues to intrigue and mesmerize a nation unused to fighting wars at home.

“I think we remain fascinated by Pearl Harbor because it was the first attack on American soil by a foreign power since the War of 1812, the worst naval catastrophe in United States history, and a landmark battle, like Yorktown or Gettysburg, that changed the course of history, in this instance by forcing the United States to play an active role in world affairs,” wrote Thurston Clarke in “Pearl Harbor Ghosts.”

Clarke’s book came out in 1991, but his words ring just as true today, with added mortality. Pearl Harbor’s defenders are in their mid-90s now, and with their passing, America is rapidly losing a touchstone to the day of infamy.

Just five crew members are still alive from the battleship USS Arizona. Although the sunken ship, a memorial and grave to most of the 1,177 killed aboard, is visited by about 1.5 million people a year, the rallying cry to “Remember Pearl Harbor” exists in the abstract three-quarters of a century later.

The successful Japanese attack on Hawaii and the United States’ response overflow with warfare superlatives and are underpinned by racial prejudices: The United States underestimated Japanese ability and military prowess. Japan underestimated American moral character and its willingness to take the fight back to Japan.

“Pearl Harbor was more than one of the most daring and brilliant naval operations of all time; it was one of the turning points in history,” noted Gordon W. Prange, Donald M. Goldstein and Katherine V. Dillon in “At Dawn We Slept.”

Many historians say it’s not possible to point a finger at any single factor for the American unpreparedness.

Prange, Goldstein and Dillon wrote that Pearl Harbor resulted from “a vast combination of interrelated, complicated and strange historical factors” including “bountiful human errors” and intelligence “badly handled” on the American side, and precise planning, tireless training, fanatical dedication, technical know-how and uncommon luck on the Japanese side.

Pearl Harbor is seen as a Japanese tactical victory leading to a strategic American victory in World War II. Had the Japanese attacked Pearl’s fuel farm and shipyard, the U.S. situation would have been far worse.

In 1941, as war clouds darkened over Asia, top U.S. military and civilian leaders thought Hawaii too far removed from Japan and too powerful to be a likely target.

On April 24, 1941, as President Franklin D. Roosevelt focused on the Atlantic and Germany and kept a wary eye on Japan, he received a Hawaii defense memo from Gen. George C. Marshall, the Army’s chief of staff.

“The island of Oahu, due to its fortifications, its garrison and its physical characteristics, is believed to be the strongest fortress in the world,” Marshall wrote. “To reduce Oahu, the enemy must transport overseas an expeditionary force capable of executing a forced landing against a garrison of approximately 35,000 men, manning 127 fixed coast defense guns, 211 anti-aircraft weapons and more than 3,000 artillery pieces.”

But the Japanese did not intend to occupy Oahu. Their aim was to neutralize the Pacific Fleet. Japan’s expansion into Southeast Asia was its real goal. It also attacked the Philippines, Wake, Guam, Singapore, Hong Kong, Midway, Malaya and Thailand.

Kimmel, the Pacific Fleet head in Hawaii, was focused on preparing for a faraway battle at sea. Lt. Gen. Walter C. Short, head of the Army’s Hawaiian Department, whose main responsibility was protection of the fleet, was fixated on the possibility of sabotage from Hawaii’s large Japanese population.

When the attack came the ships weren’t ready for it, and planes were parked wingtip to wingtip on airfields to make them easier to guard. A slow, surreal realization dawned that this was not a drill.

“What was happening was the inconceivable. And when you are dealing with the inconceivable, then there is a moment when you can’t believe it’s happening,” said Daniel Martinez, chief historian for the World War II Valor in the Pacific National Monument.

Terrible death reached throughout the harbor from the passing Japanese planes.

The concussion of the 1,760-pound bomb that destroyed the Arizona put out fires on the adjacent repair ship Vestal. “It also sent tons of debris down on her decks — parts of the ship, legs, arms and heads of men … even living men. The explosion flung overboard about 100 men from Vestal,” the authors of “At Dawn We Slept” said.

Through it all, U.S. military men fought back as best they could.

“We have incredible bravery of men trying to defend their air bases and being killed or wounded during the process — and they were doing it despite all hell breaking loose,” Martinez said.

In Pearl Harbor, “sailors are trying to protect their ships,” he said. “Along Battleship Row, if you are an outboard ship, you are taking a tremendous amount of damage from torpedo attack.”

Martinez added, “The kind of valor that was displayed was in the highest traditions of the military that day.”