PARIS — Countries signing up to buy the joint strike fighter have all said they are interested in a block buy that could see commitments to purchase 500 of the aircraft, a Lockheed Martin official said on Monday.

"They have all said they are interested," said Lorraine Martin, Lockheed's F-35 program manager, after a briefing on the program at the Paris Air Show on Monday.

"There are some countries that do this all the time, they usually do multi-year," she said. "There [are] some countries, like Japan, that have just passed legislation that enables them to do this and they have never done it in the past."

Pentagon procurement chief Frank Kendall last month backed multi-year, bulk purchases of the JSF by the US and other countries.

Rather than relying on nations signing up to buy aircraft from individual production runs, known as low rate initial productions, Lockheed and the US government will now ask countries to sign up to a block buy comprising aircraft from LRIPs 12,13 and 14, which would be ordered in the fiscal years of 2018-2020.

Martin said the US Congress would want to see big savings thanks to the block buy before approving it.

"They are expecting significant cost savings. The US Congress often looks for around 10ten percent," she said.

Savings would flow from the bulk buy, she added.

"The ability to tell the supplier base that you are going to get 400 plus, almost 500 aircraft, can have a huge impact," on savings, she said. The block buy would be around 460 aircraft, rising to around 500 if Canada and Denmark joined.

Knowing they were in line for savings might sway the two potential buyers, she said. "They can get a cheaper aircraft and that might help them with other stresses they might have," she said.

Martin declined to say what deadline would be given nations to decide on backing a bulk buy, but suggested it could be around a year.

During her briefing, Martin said that by 2018, half the JSFs ordered would be for partner nations. By 2019, she added, Lockheed Martin would try and reduce the price per plane to $80 million, "a fifth generation aircraft for the same price as a fourth generation."