Australia will make one of its biggest ever military purchases with a $12 billion order for 58 Joint Strike Fighters in a move that will lift the nation's air combat power to among the world's most advanced.

Prime Minister Tony Abbott will announce the planned purchase in Canberra on Wednesday, confirming that Australia will join the United States and a select few other countries in adopting the fifth-generation stealth fighter as the backbone of its air combat power.

On top of the two fighters that Australia has already paid for, and a further 12 that have been ordered, the large new purchase will deliver the Royal Australian Air Force three squadrons of the planes and cement its place as the dominant air power in the region.

The government is keeping open the option of buying another squadron of up to 24 fighters, taking Australia's fleet of the cutting-edge planes close to 100.

The first Joint Strike Fighter – also called the Lockheed Martin F-35 Lightning II – will be delivered in 2018 and begin service with the RAAF in 2020.

"The fifth-generation F-35 is the most advanced fighter in production anywhere in the world and will make a vital contribution to our national security," Mr Abbott will say on Wednesday.

"Together with the Super Hornet and Growler electronic warfare aircraft, the F-35 aircraft will ensure Australia maintains a regional air combat edge. The F-35 will provide a major boost to the Australian Defence Force's intelligence, surveillance and reconnaissance capabilities."

Defence Minister David Johnston said on Wednesday that the purchase would give Australia’s air combat capability ‘‘the sort of technological edge that it must continue to have’’.

He defended the billions in spending - less than a month before Treasurer Joe Hockey delivers a budget with expected cuts to health and welfare, saying the money for the fighters had been put aside since the government’s initial order of 14 aircraft.

‘‘The money is contained within the defence budget in the outyears of the budget and beyond,’’ Senator Johnston told ABC radio. ‘‘We are committed to defending Australia with the best available platforms. This clearly is a regionally dominant and cutting-edge platform that will see Australia right out to 2050.’’

Opposition leader Bill Shorten backed the purchase, saying the previous Labor government believed the Joint Strike Fighter was the ‘‘right way to go’’.

When asked if the order should be scaled back given the tough budget climate, Mr Shorten said the fighter program was a long term-investment.

‘‘These defence purchases are necessary for our forward security plans over a number of decades,’’ Mr Shorten told ABC radio.

The lifetime cost of the new batch of fighters,  which includes maintenance, weapons and spares, will reach $12.4 billion, making it one of Australia's most expensive ever military acquisitions alongside the Collins Class submarine and the long-retired aircraft carriers.

The announcement is also a win for the RAAF bases at Williamtown in NSW and Tindal in the Northern Territory, which will be the home bases for the squadrons. They will need about $1.6 billion in new facilities and infrastructure, Mr Abbott will announce.

The JSF will replace the ageing Hornet F/A-18, which is due to be retired from 2022. It means the RAAF will have a mixed fleet of fighters for the foreseeable future, with the JSF operating alongside 24 Super Hornets and 12 Growler radar-jamming aircraft.

The purchase continues the direction set out by the previous Labor government's 2013 Defence White Paper, which foreshadowed three operational squadrons beginning from 2020.

While most experts say the Joint Strike Fighter is set to be the most advanced fighter for years to come, critics have pointed out the many flaws, delays and cost overruns that have emerged during its development.

The Pentagon's Joint Strike Fighter boss, Lieutenant-General Chris Bogdan, said during a recent visit to Australia that many problems were still being ironed out, particularly the complex software – requiring more than 8 eight million lines of code – which he said was ''still a risky, risky business''.

He also said the planes were still unreliable and needed too much maintenance, with "pieces and parts ... coming off the airplane way too regularly because they are breaking".

Critics have also pointed out the new stealth fighters are actually less manouevrable manoeuvrable than some older planes, though supporters say it will never need to turn sharply because it will have shot down any enemy plane before it is seen.

Mr Johnston said the purchase would also provide a boost to the Australian defence industry.

"As a result of the Howard Ggovernment’s decision to join during the development phase, the Australian defence industry has been awarded over $355 million in work and stands to win well in excess of $1.5 billion in JSF-related production and support work over the life of the programme – creating long-term advanced manufacturing and engineering jobs," he said.

KEY FACTS

Maker Lockheed Martin

Cost per plane about $95 million, not including weapons

Strengths steath capability, advanced computer power, able to talk to all allied military systems around it

Weaknesses Not particularly manoeuvrable, faced problems flying during lightning storms

Weapons guided bombs, sidewinder missiles, radar-jamming electronic warfare capabilities

Special exterior features radar absorbing outer skin

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