According to a Kyodo/Reuters articles sources are now saying that Japan and the United States are drawing up plans for joint operations responses to any threat that China may pose to the Senkaku Islands. This was discussed in the Japan Times and according to the article, was from government sources and released on Saturday.
Japan and the US have a treaty that underscores America`s commitment to defend Japan under article 5 of said security treaty. Naturally this security treaty extends to the Senkaku Island chain, a base for food resources for the Japanese during the 1930s and 1940s.
The plan has specific scenarios that direct the Maritime Defense Forces on handling situations such as Chinese fishermen landing on the island to take control. Officially, the United States has had no opinion on the control of these islands but it is clear that Japan wants to bring the US into a relationship that will deliver US cooperation. According to sources, the Self-Defense Forces have action plans made independently by Japan but would bring in the US for air strikes in case action is needed.
Keep in mind that the US and Japan have specific combined operations plans for an emergency on the Koren Peninsula as well as other situations. Currently Japan and the US carry out a joint exercise called Keen Sword Exercise, done biannually. This exercise combines 57,000 troops who are Navy, Air Force and Army as well as others. Also, the US and Japan conduct joint submarine drills to counter the Chinese expansion into the South China Sea and near Japanese territory. China continues to expand in the region, so there is growing concern for Japan, the US and South Korea as well as India for containment and a joint response.
The US has stationed submarines in bases in Japan and has put the Reagan, the largest US aircraft carrier with 5,000 troops and 90 F-18 Hornets as part of a massive strike force in the region. Canada has also participated in such drills, but in a support role.