The Global Hawk was brought to the US Misawa Air Base from Guam "to support US intelligence, surveillance, and reconnaissance missions and contingency operations throughout the Pacific theater," America's air force said on its website.
The high-altitude reconnaissance plane is scheduled to operate until October, it said, adding that the deployment of the aircraft is partially aimed at monitoring typhoons that frequently hit Guam during summer.
It is also believed it will be used to monitor North Korea and China at a time when Pyongyang's nuclear and missile development programme and Beijing's maritime assertiveness have raised security concerns in Japan, local media reported.