The cremated remains of the astronaut, who died at 82 in August, were rested at the sea after a public memorial attended by hundreds of mourners.
Armstrong's cremated remains were sent into the Atlantic Ocean during a burial-at-sea service aboard the USS Philippine Sea, NASA said.
The ceremony was attended by his wife Carol Armstrong, according to CNN.
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, including Armstrong's Apollo 11 crewmates Buzz Aldrin and Michael Collins.
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.