Both participants in a Pentagon X-plane project to develop a heavy-lift seaplane are advancing toward the build stage of the effort.

General Atomics Aeronautical Systems and Aurora Flight Sciences on 27 July each received contracts valued around $20 million to fund continued development efforts for the Liberty Lifter – a wing-in-ground-effect seaplane meant to carry loads of 90,000kg (200,000lb) or greater.

The Pentagon’s secretive technology incubator – the Defense Advanced Research Projects Agency (DARPA) – is overseeing the competition.

“The planned Liberty Lifter demonstrator will be a large flying boat similar in size and capacity to the [Boeing] C-17 Globemaster III transport aircraft,” DARPA says.

The agency announced the Liberty Lifter effort in May 2022. The goal is to produce a heavy-lift demonstrator aircraft capable of landing and taking off without a land- or ship-based runway. The Pentagon wants the still-conceptual aircraft to be capable of reaching altitudes of 10,000ft, using ground effect to take off.

Boeing subsidiary Aurora and unmanned air vehicle (UAV) maker General Atomics were selected by DARPA as the programme’s final participants in February. The firms had previously won contracts worth $5.6 million and $7.9 million, respectively, to begin design and engineering work.

The 27 July contract announcement significantly raised DARPA’s commitment to the Liberty Lifter project, as the agency exercised options on both companies’ initial proposals. General Atomics will receive $21.5 million to fund additional work, while Aurora’s additional share is $19.5 million.

DARPA hopes to begin the next phase of the programme in mid-2024, which will include detailed design, manufacturing and flight demonstration of full-scale Liberty Lifter craft.

“The two teams have taken distinctly different design approaches that will enable us to explore a relatively large design space during Phase 1,” DARPA’s Liberty Lifter programme manager Christopher Kent noted in February.

The agency revealed that the General Atomics team selected a twin-hull, mid-wing design to “optimise on-water stability and seakeeping”. 

“It employs distributed propulsion using twelve turboshaft engines,” DARPA said of General Atomics’ design.

Aurora’s concept, DARPA says, “more closely resembles a traditional flying boat, with a single hull, high wing and eight turboprops for primary propulsion”.

Interest in water-capable aircraft has been surging within the US military, as the Pentagon seeks to restructure its forces for a potential conflict in the Indo-Pacific region.

In addition to Liberty Lifter, DARPA is funding a competition to develop an autonomous UAV capable of operating from ships and small islands using vertical take-off and landing. Nine manufacturers are participating in that effort.

US Special Operations Command is also exploring the possibility of developing a seaplane variant of Lockheed Martin’s C-130 turboprop transport. The command is partnering with Japan to learn from the country’s experience with the ShinMaywa US-2 maritime cargo aircraft.

Spurred by interest in maritime mobility aircraft, Florida-based Catalina Aircraft on 25 July announced it will relaunch production of the iconic Consolidated PBY Catalina flying boat. That aircraft saw military and commercial passenger service during World War II.

Catalina, which holds the regulatory type certificates for the PBY in both the USA and Canada, plans a modernised version of the venerable flying boat, including updated engines and modern avionics.

Another start-up – Rhode Island-based Regent Craft – is marketing its ground-effect “seagliders” to the Pentagon as a potential solution for high-speed logistics in the maritime environment of the Indo-Pacific. Regent has financial backing from Lockheed’s venture capital fund.