TOKYO - Japan's defence planners are seeking their biggest budget ever for the coming fiscal year to pay for stealth fighters, drones and a hi-tech submarine, as Prime Minister Shinzo Abe bolsters the military.

Japan mulls enhancing missile detecting capability

The Defense Ministry on Friday requested a 3.5 percent increase to 5.05 trillion yen ($48.7 billion) for the year starting next April. If approved, this third increase in a row will more than reverse the decade of cuts that Abe ended after coming to office in December 2012.

The hawkish premier, taking a more assertive stance on national security, has also ended a ban on Japanese soldiers fighting abroad and eased curbs on weapons exports.

By testing the constraints of Japan's pacifist postwar Constitution, Abe has angered some neighbours, especially Beijing, which accuses him of reviving the nation's wartime militarism.

Japan's Defense Ministry wants to buy six F-35 stealth fighters from Lockheed Martin Corp as well as 20 P-1 patrol planes from Kawasaki Heavy Industries Ltd - a bulk purchase to cut per-unit cost.

The government says procurement reform, including bulk purchases for multi-year projects, will save 700 billion yen over five years.

Japan's shopping list

The ministry is also seeking 64.4 billion yen for an upgraded Soryu class submarine that can stay submerged far longer than the boat of the same class it requested for this fiscal year for 20 percent less.

The new sub has a propulsion system using long-running lithium-ion batteries, replacing one that used liquid oxygen to run a diesel engine, allowing it to stay underwater for around two weeks. The new design allows a "significant extension to the submarine's ability to stay submerged," said a ministry official.

Australia has said it is interested in the Soryu design as a possible replacement for its Collins class subs, which need to suck air through a snorkel at the surface when they use their diesel engines while submerged.

Japan's shopping list also includes unmanned surveillance planes and tilt-rotor aircraft that take off and land like a helicopter but fly like a plane, as Japan aims to boost its monitoring and troop-deployment capabilities.

The ministry does not specify which models of tilt-rotor aircraft and unmanned drones it has in mind because talks with potential suppliers are still going on, but the V-22 Osprey, built by Boeing Co and Bell Helicopter, is the only tilt-rotor plane in military use - including by US forces in Japan.

Besides the cutting-edge weapons, the budget request is boosted by the planned replacement of ageing government planes, used for purposes like the prime minister's overseas trips - akin to the US president's Air Force One - with two of Boeing's 777-300ER jets.

When expenses for the new government planes and costs associated with the realignment of US forces in Japan are excluded, the budget request comes to 4.9 trillion yen, up 2.4 percent from this year.

The Defense Ministry is also eyeing North Korea, seeking its seventh destroyer equipped with the Aegis ballistic-missile defence system.

"We will fortify our system of defending the whole of our country continuously and in a multi-layered fashion against ballistic missile attacks," the ministry said in a statement.

Much of the Japanese archipelago sits within the range of North Korea's mid-range Rodong missiles. The ministry's latest white paper calls Pyongyang's military activity a grave destabilising factor for Japan and the rest of the world.

The submission of the initial budget request will be followed by a series of negotiations between the Defence and Finance ministries ahead of the compilation of the government's budget bill at the end of the year.