Armstrong's cremated remains were sent into the Atlantic Ocean during a burial-at-sea service aboard the USS Philippine Sea.
His wife, Carol Armstrong was presented an American flag at the ceremony aboard the aircraft carrier on Friday that included a bugler and rifle salute.
Armstrong commanded the Apollo 11 spacecraft that landed on the Moon July 20, 1969, and was the first astronaut to exit the spacecraft. He was followed to the lunar surface by Buzz Aldrin.
"That's one small step for (a) man, one giant leap for mankind," Armstrong had said at the time.
Armstrong, who died August 25 at age 82, was an aviator in the US Navy before becoming the first person to walk on the moon, having flown 78 combat missions during the Korean War.
A day before his internment at sea, an inter-faith meeting was held for him at the Washington National Cathedral, attended by about 2,500 people.
The memorial service at the cathedral also brought together dignitaries, community and political leaders, Armstrong's family members, and members of the NASA family, including current and former astronauts.