The crew of the aircraft carrier Ronald Reagan, on a humanitarian mission to Japan, received a month's worth of radiation in about an hour, The New York Times reported.
Citing unnamed government officials, the newspaper said the ship passed through a radioactive cloud from damaged nuclear reactors in Japan when it approached the country on its humanitarian mission.
Japan has been battling to control two overheating reactors at the ageing Fukushima plant after the cooling systems were knocked out by Friday's 8.9-magnitude quake and the resulting tsunami that swallowed up whole towns.
A new explosion at the plant hit the country Monday as experts raced to avert a catastrophic meltdown in the wake of the quake and tsunami.
US helicopters flying missions about 60 miles (96 kilometers) north of the damaged reactors became coated with radioactive dust that had to be washed off, the report said.
There was no indication that any of the military personnel had experienced ill effects from the exposure, the paper said.
But the episodes showed that the prevailing winds were picking up radioactive material from crippled reactors in northeastern Japan, The Times noted.