The exercise was also the first to be held in Hokkaido, as an effort to strengthen the US-Japan alliance by training together on unfamiliar ground, Reuters reported.
Although the drills are not related to the latest tension on the Korean peninsula, it is taking place as unease between North Korea and the US are escalating and with US troops based in Okinawa, where the bulk of US forces in the region are based.
The 18-day live fire exercise which includes rocket artillery drills and live-fire operations will run through August 28 and will involve 3,500 troops.