The Diaoyu Islands are a group of uninhabited islands located roughly due east of mainland China, northeast of Taiwan, west of Okinawa Island, and north of the southwestern end of the Ryukyu Islands. They are currently controlled by Japan, which calls them Senkaku Islands. Both China and Taiwan claim sovereignty over the islands.
Osprey troop transporters on Japan's buy list amid fears over China
Move to purchase US-built aircraft comes as Tokyo shifts defence focus to island territories
Julian Ryall in Tokyo
Japan's defence ministry is pushing ahead with plans to purchase the controversial MV-22 Osprey aircraft, widely seen as the best way of rapidly transporting troops to potential hot spots.
The US-built Osprey has a top speed of 530 km/h - almost double that of current transport helicopters - and a 3,900 kilometre range that is five times the range of the CH-46 Sea Knight helicopter the United States is phasing out of service in favour of the Osprey.
The features are seen as being crucial as Japan pivots away from the ground threat posed by the former Soviet Union during the cold war to a more flexible defence based on the rapid deployment of troops to counter a threat to Japanese territory in the southwest of the island chain.
In recent years, Tokyo has perceived that threat as coming from China coveting Japanese islands that are part of Okinawa.
In spending requests for 2014 that were lodged this week, the defence ministry is seeking 100 million yen (HK$7.82 million) to study the purchase and capabilities of the Osprey. If all goes well the ministry will seek to purchase up to 20 Ospreys in 2015.
The aircraft is a hybrid with tilting rotors that allow it to take off vertically like a helicopter, while flying like a standard plane.
It can seat 32 troops and has an optimum cargo load of just over nine tonnes, four times greater than the helicopters it is replacing in the US military. It can also operate from aircraft carriers and be refuelled during flight.
But the Osprey has been deeply unpopular in Okinawa even before it was first deployed by US marines there last year, with protesters claiming the aircraft were unsafe. The US said teething problems had been largely solved and recent incidents involving Ospreys were the result of "pilot error".
In total, the defence ministry has requested 4.89 trillion yen for the financial year starting in April.
Tokyo has also committed itself to purchasing the F-35 interceptor jet to replace its fleet of ageing F4 Phantoms and put it ahead of anything the Chinese or Russian air forces can deploy.
The feasibility of deploying Global Hawk drones is also being considered as early as 2015, along with two amphibious vehicles, while steps are under way to create a new unit based on the US marines. Other funding will be earmarked for cyber- and missile defences.