MANILA - President Rodrigo Duterte has approved a 5-year plan to spend P300 billion ($5.6 billion) to modernize the outdated military, defense officials said on Wednesday.

A previous 15-year upgrade plan failed to take off in the mid-1990s, leaving the Philippines with outdated hardware, including warships from World War 2 and helicopters used by the United States in the Vietnam War.

"We have the go signal now to buy brand-new equipment, like fighters, drones, light tanks, radar, an additional frigate and a submarine to boost our defense capability," said a defense official, who declined to be named because he is not authorized to speak to media.

• Duterte: No more secondhand hardware for military

The previous administration of Benigno Aquino III spent about a third- P91 billion ($1.7 billion) - on the military during his 2010-2016 term in office, mostly on secondhand ships and planes.

Duterte approved the P300-billion modernization plan at a meeting with top defense and military officials last month.

A senior general said Duterte had approved 33 modernization projects, with a focus on domestic security and protecting the vast maritime borders of the archipelago.

"We're putting a premium on unmanned aerial vehicles, long-range patrol aircraft, offshore patrol ships and an electric-diesel submarine," he told Reuters.

The military is bent on preventing another Islamic State-inspired insurgency after rebels seized Marawi, the country's only Islamic city, for five months last year.

• Duterte: Nobody won the war in Marawi

The Philippines also faces a challenge in South China Sea, a strategic waterway most of which is claimed by China, which has built military outposts there.

• Duterte wants to assert PH rights over S. China Sea but warns of 'great loss'

Besides the Philippines and China, Brunei, Malaysia, Taiwan and Vietnam also have rival claims on the area, through which $3 trillion worth of sea-borne goods pass every year.

Manila had planned to acquire four submarines after 2023, but the plan could be accelerated to boost the Navy's regional capabilities, said Arsenio Andolong, a defense department spokesperson

"We want to get submarines as soon as possible," he said.

Duterte had set aside $1 billion for new helicopters and light tanks, but no purchases have been made yet.

The Philippines has received donated military hardware from Australia, China, Japan, Russia and the United States, mostly to assist in disaster response and fighting militants and pirates.