Seventy-five years ago the President of the United States, Franklin Delano Roosevelt, addressed a joint session of Congress and spoke words that even today seem chilling. “Yesterday, December 7th, 1941—a date which will live in infamy—the United States of America was suddenly and deliberately attacked by naval and air forces of the Empire of Japan.” Roosevelt’s prediction could not have been more accurate. The December 7th attack on the United States naval base at Pearl Harbor, which crippled the U.S. Pacific Fleet, remains a day of national mourning. Every year the nation pauses to solemnly remember that attack and the thousands injured and killed as it unfolded.

Among those defending Pearl Harbor on that fateful day were members of two National Guard units, California’s 251st Coast Artillery Regiment and Hawaii’s 298th Infantry Regiment. Both of these units were part of a build-up of American military forces begun in August of 1940. More than 400,000 National Guardsmen were called up, effectively doubling the size of the U.S. Army. In the aftermath of Pearl Harbor, American forces continued to build, and the Guard contributed 19 divisions to the war effort. Reserve forces also became key contributors. Almost one of every four Army officers—more than 200,000 of the 900,000 Army officers who served during the war—was an Army Reservist.

The architect of the attack on Pearl Harbor, Japanese Admiral Isoroku Yamamoto, seemed to sense that the attack would end in disaster for Japan. In a letter to a friend who thought Japan had just won a great victory, he wrote, “A military man can scarcely pride himself on having ‘smitten a sleeping enemy’; it is more a matter of shame, simply, for the one smitten. I would rather you made your appraisal after seeing what the enemy does, since it is certain that, angered and outraged, he will soon launch a determined counterattack.”

Admiral Yamamoto was right. The day following the attack the United States declared war on Japan. By war’s end the Japanese military had suffered over two million deaths, and as many as 800,000 Japanese civilians had died. Japan paid a terrible price for its attack on Pearl Harbor.

Seventy-five years later the world has changed. Japan rebuilt its nation and is now a strong ally of the United States. But we will never forget Pearl Harbor. The National Guard’s motto “Always Ready, Always There,” reminds us that we must always be alert to potential danger, and be ready to defend ourselves. It is a state-of-mind that has existed for 380 years of National Guard service and 108 years of the Army Reserve. And it is the enduring lesson of “a date which will live in infamy.”