The helicopter carrier Izumo will leave the mother port of Yokosuka, south of Tokyo, on Monday and join the US supply ship to escort it further into the western Pacific, the leading Asahi Shimbun daily and Jiji Press reported citing unnamed government sources.
It will be the first deployment - outside of troop exercises - to protect the US fleet after Prime Minister Shinzo Abe expanded the country's military capabilities in 2015, though they remain restricted under Japan's pacifist constitution.
The US supply ship is expected to support America's naval fleet in the Pacific, possibly including the aircraft carrier USS Carl Vinson, which remains on high alert over North Korea's ballistic missile firings, the reports said.
Japanese naval officials declined to comment on the reports.
Earlier this week, the US carrier had joint drills with Japan's naval forces.
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.
North Korea's state media has said the North's military is capable of sinking the US aircraft carrier with a single strike.
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.
US President Donald Trump, who has warned of a "major conflict" with North Korean leader Kim Jong-Un's regime, said the latest test was a pointed snub to China - the North's main ally and economic lifeline.
"North Korea disrespected the wishes of China & its highly respected President when it launched, though unsuccessfully, a missile today. Bad!" Trump tweeted.