The United States is examining the possible development of a twin-engined warplane to be known as the F-55, as well as an upgrade to its Lockheed Martin F-22 Raptor called the F-22 Super, U.S. President Donald Trump said on Thursday.

Trump was speaking at a meeting of business leaders including the heads of Boeing and GE Aerospace in Doha, a day after announcing a string of business deals including an order from Qatar for 160 Boeing commercial jets.

Trump referred to the proposed F-55 as both an upgrade to the Lockheed Martin F-35 and a separate new development.

He also highlighted the role of a new air dominance platform called the F-47, recently awarded to Boeing, and said the United States was simultaneously looking at upgrading the stealth fighter that it is designed to replace, the F-22.

"We're going to do an F-55 and - I think, if we get the right price, we have to get the right price - that'll be two engines and a super upgrade on the F-35, and then we're going to do the F-22," Trump said.

"I think the most beautiful fighter jet in the world is the F-22 but we're going to do an F-22 Super and it'll be a very modern version of the F-22 fighter jet," he said.

"We're going to be going with it pretty quickly," he added.

Trump's comments came weeks after he awarded Boeing the contract for the F-47 - a replacement for the F-22 stealth fighter featuring a crewed aircraft flanked by drones and seen as America's most advanced or sixth-generation fighter.

NAVY JET?

The future of the radar-evading F-22, which is designed to combat other fighters, has been fiercely debated for years as Congress blocked plans by the Air Force to speed up retirements to focus on the next generation blueprint that became the F-47.

Analysts said it was not immediately clear how Trump's list of potential developments fitted into known programmes and spending plans, or the timing of existing programmes.

Agency Partners aerospace analyst Nick Cunningham said the F-55 may refer to the F/A-XX programme, intended to replace the U.S. Navy's ageing Boeing F/A-18 Super Hornet fleet with the service's own sixth-generation stealth fighter during the 2030s.

The Navy and Congress are battling with the administration to keep the plans moving forward, Reuters reported on Wednesday. Announcement of a winning bidder had been expected as early as March.

Any significant upgrade to the out-of-production F-22 would be costly, while Trump's reference to two engines implies the F-55 would not be closely related to the single-engined F-35, analysts said.

"Adding an engine to the F-35 makes it a new aircraft," UK-based defence analyst Francis Tusa said.

Lockheed Martin is in the midst of a delayed technology and software upgrade for the F-35 to boost displays and processing power.

CEO James Taiclet also told analysts last month that Lockheed was looking at ways of applying co-funded technology that was developed for its losing bid for the F-47 contract to the F-35, delivering 80% of the capability for half the cost.

(Reporting by Andrew Mills, Nayera Abdallah, Tim Hepher; Editing by Alex Richardson and Ros Russell)