Pearl Harbor in Honolulu was attacked 71 years ago, on Dec. 7, 1941. Social-media users have shared pictures of Pearl Harbor on Instagram and Twitter, ranging from past to present, to commemorate one of the most tragic days in U.S. history.

Remnants of that gruesome day continue to exist, reminding Americans of the attack that constituted the first U.S. battle of World War II.

U.S. warships remain at Pearl Harbor to this very day. The USS Arizona Memorial marks the resting place of many of the sailors killed on the battleship when it was sunk during the attack, while the USS Missouri, the last battleship commissioned by the U.S. (in 1944), is moored less than a quarter-mile away.

The USS Missouri is the ship where one of the most significant events of World War II took place: On Sept. 2, 1945, Japanese Foreign Minister Mamoru Shigemitsu signed two copies of the Instrument of Surrender on behalf of Emperor Hirohito and the Empire of Japan. The two copies still sit on the Missouri as a reminder of the historic event that took place on her deck.

Anyone who has visited the USS Arizona Memorial at Pearl Harbor can attest to how eerie it is to see the battleship at the bottom of the sea, where the USS Utah also lies, another victim of the attack that brought the U.S. into World War II.

Flowers continue to be brought to the memorial, even 71 years after the first bombs were dropped that killed an estimated 2,390 American military-service members and 49 civilians, according to the Associated Press.

A ship recently named after a Pearl Harbor-based Navy SEAL killed in Afghanistan -- the USS Michael Murphy -- sounded its whistle on Friday to begin a moment of silence at 7:55 a.m., the exact time the bombing began in 1941, AP reported.

""Let us remember that this is where it all began. Let us remember that the arc of history was bent at this place 71 years ago today and a generation of young men and women reached deep and rose up to lead our nation to victory," Rhea Suh, an assistant secretary of the U.S. Interior Department, told the assembled crowd. "Let us remember and be forever grateful for all of their sacrifices."

About 30 survivors attended the ceremony Friday, AP noted, many of whom were using canes or walkers and in their 90s.