The United States on Wednesday marked the 70th anniversary of the Japanese attack on Pearl Harbor that catapulted the U.S. into World War Two.

About 120 survivors of the attack attended a ceremony at Pearl Harbor itself, in the Pacific island state of Hawaii. Some 3,000 people observed the event at a memorial structure straddling the sunken remains of the USS Arizona battleship.

They held a moment of silence at 7:55 in the morning , the exact moment Japan's Imperial Navy began the surprise attack.

Memorial events marking the December 7,1941 attack are being held throughout the U.S., with flags flying at half-staff to memorialize the dead.

In a statement marking the day, U.S. President Barack Obama paid tribute to those whose died, saying that “their tenacity helped define the greatest generation.”

The attack by the Japanese on the U.S. naval base at Pearl Harbor was unprovoked. Four U.S. battleships sank or capsized, several hundred warplanes were destroyed and more than 2,400 servicemen, women and civilians died. It was the most devastating foreign attack on U.S. soil until September 11, 2001.

Many Americans draw a comparison between the attack on Pearl Harbor and the attacks in 2001. A spokesman for the Pearl Harbor Navy Yard says the comparison keeps the memory of Pearl Harbor alive for a new generation.

The U.S. declared war on Japan the day after Pearl Harbor was attacked. On December 11, 1941, Japan's Axis partners Germany and Italy declared war on the U.S., marking the nation's entry into the global conflict.