If you made a stop to the post office, the DMV or any other federal building on Wednesday, you may have noticed that flags are flying at half-staff.

Flags are regularly lowered to half-staff (or half-mast, if you’re on a ship or a naval station) to commemorate important moments in American history or honor Americans who have lost their lives.

Dec. 7 is one such day that falls under both categories. It’s the anniversary of the Japanese attack on Pearl Harbor on Dec. 7, 1941.

More than 2,300 military service members and dozens of civilians were killed on that day; a thousand more were injured.

Each year, the United States observes National Pearl Harbor Remembrance Day to remember those lost in what was a flashbulb moment in world history that marked the U.S. formally joining into World War II.

Prior to the surprise attack on the Hawaiian military base, the United States officially took a neutral position in the ongoing violent war abroad.

President Joe Biden, like his predecessors before him, signed a proclamation to order flags to be flown at half-staff as part of National Pearl Harbor Remembrance Day.

In his proclamation, the president wrote, “We reflect on the resilience of America’s Armed Forces, who withstood the attack and built the most capable fighting force the world has ever known. In the wake of tragedy, these brave women and men — the Greatest Generation — answered the call to defend freedom, justice, and democracy across the Pacific, throughout Europe, and around the globe.”

Biden continued, adding that World War II and America’s involvement brought “victory over the forces of fascism” and helped establish the rules of international order.

The president urged all “Federal agencies, interested organizations, groups, and individuals” to fly their flags at half-staff in honor of the lives lost during the attacks on Pearl Harbor.

“I encourage all Americans to reflect on the courage shown by our brave service members that day and remember their sacrifices. I ask us all to give sincere thanks and appreciation to the survivors of that unthinkable day,” Biden said.