The Philippines will buy three new C-130J-30 Super Hercules planes for its air force, the defence ministry said Tuesday, nearly doubling its fleet for large transport aircraft.

The acquisition — part of a modest military modernization program that began more than a decade ago — comes as its longtime US ally seeks to counter China's growing assertiveness in the South China Sea.

Philippine forces are also fighting a lingering communist insurgency and armed militants in its Muslim-populated south.

"The addition of the C-130J-30 to the inventory is a significant leap forward in terms of achieving a credible defense posture," the defense ministry said in a statement that did not disclose the value of the deal.

US manufacturer Lockheed Martin has been contracted to deliver two of the aircraft in 2026 and the third in January 2027, the statement said.

The new planes can carry up to 128 combat troops or 92 paratroopers each.

Lockheed Martin's website described the model as an "affordable" and "stretch version" of its C-130J, with a maximum payload of nearly 20 tons.

The Philippine air force currently operates four C-130 planes, an older version of the airlifter, a spokeswoman told AFP.