Prime Minister Tony Abbott's order to examine turning the navy's amphibious assault ships into aircraft carriers for jump jets will require a major rethink by Defence, top military brass have indicated.

Facing a Senate hearing on Monday, Defence chiefs said little work had so far been done on the possibility of buying a short take-off and vertical landing variant of the Joint Strike Fighter - an idea that has seized the interest of the Prime Minister.

Tony Abbott with a replica of a Joint Strike Fighter. Credit:Alex Ellinghausen

Under questioning by Labor defence spokesman Stephen Conroy, defence chiefs confirmed for the first time that Mr Abbott had asked them to look at the merit of buying the F-35B jump jets under the forthcoming Defence White Paper and accompanying Force Structure Review.

Under the proposal, they would be flown from the navy's two Landing Helicopter Dock amphibious assault ships, which are due to come into service over the next 12 to 18 months.