The guided-missile destroyer USS Benfold was participating in a scheduled towing exercise in Sagami Bay on Saturday when the Japanese tug lost propulsion, according to the US 7th Fleet.
The incident came as Japanese and US forces take part in a 10-day joint naval drill until November 26 in a show of force aimed at North Korea, whose nuclear ambitions dominated US President Donald Trump's recent Asia trip.
"No-one was injured on either vessel and Benfold sustained minimal damage, including scrapes on its side, pending a full damage assessment," a statement from the 7th fleet said late Saturday, adding the warship remained at sea under her own power.
"The Japanese commercial tug is being towed by another vessel to a port in Yokosuka," southwest of Tokyo, it said.
The Japanese coastguard said the tug lost control and drifted into the warship as a rope got caught in its propeller, but confirmed there were no injuries.
The 7th Fleet has been involved in more than one deadly collision in Asia so far this year.
The USS John S. McCain collided with a tanker off Singapore in August, killing 10 sailors and injuring five others.
Two months earlier in June, the USS Fitzgerald and a cargo ship smashed into each other off Japan, leaving seven sailors dead.
There were also two more, lesser-known incidents. In January USS Antietam ran aground near its base in Japan, and in May, USS Lake Champlain collided with a South Korean fishing vessel.
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