Japan and the US have begun the annual Yama Sakura joint manoeuvre on the south-western island of Kyushu, Japan, to enhance the nations' ability to fight together.
About 1,500 US and 4,500 Japanese military personnel are participating in the command post exercises, which will last until 3 February 2011.
The exercise involves simulations of ballistic missile attacks, special forces warfare and an invasion of Japan's southernmost main island, rather than real-world deployment of troops.
Japanese Commander Lieutenant General Shunzo Kizaki said the exercises were not directed towards any particular threat but to contribute to Japanese troops' ability to deter and defend.
The US has deployed 50,000 US troops throughout Japan under a mutual security treaty and trains intensely with its Japanese counterpart, according to the Canadian press.