The Carl Vinson arrived in the Sea of Japan and kicked off a joint drill with the South Korean navy on Saturday, hours after North Korea launched a ballistic missile in apparent defiance of the US.
Japan has dispatched its biggest warship, Izumo, to escort USA supply vessels including the Carl Vinson aircraft carrier group.
Japan's helicopter carrier, the Izumo, is 249 meters long and can carry up to nine helicopters, according to the Japan Times.
The latest missile launch, which South Korea said was a failure, ratchets up tensions on the Korean peninsula, with Washington and Pyongyang locked in an ever-tighter spiral of threat, counter-threat and escalating military preparedness.
To ensure success of their escort mission, the Japanese seamen have been authorized the "minimum necessary use of weapons", to deter any attacks amid North Korean threats to sink United States ships, the Japan Times reports.
A possible missile strike and what to do about it have dominated TV talk shows and other media in Japan in recent weeks as regional tension has spiked, with the North Korean regime continuing to test-fire rockets and President Donald Trump sending an aircraft carrier to nearby waters in a show of force.
But shortly after the plan was announced, reports emerged that the carrier group was actually heading in the opposite direction of the Korean Peninsula, moving southwest to join the Australian Navy for joint exercises in the Indian Ocean. "We strongly condemn such acts", Abe told reporters in London on Saturday.
Meanwhile, a 70-year-old housewife in Yokosuka, Kanagawa Prefecture, said, "We don't know what North Korea will do and that scares me".
Meanwhile, the Japanese public remains divided over whether to amend the war-renouncing Article 9 of the Pacifist Constitution, which marks its 70th anniversary on Wednesday.
Prime Minister Shinzo Abe's government has expanded the role of the Self-Defense Forces through the new legislation to more actively contribute to regional and global security issues, but the move has been controversial in the country, where many people cherish the pacifism embedded in the post-World War II Constitution.
North Korea is "mostly bluffing its military capability, and the missile scare is further hyped up largely by TV", said Hiroki Fujii, a 40-year-old utility employee who lives near Yokota.