Amid continuing uncertainty over delays to the F-35 Joint Strike Fighter, the Australian government has opened up a long-anticipated study with the U.S. into the “potential purchase” of 24 additional Boeing F/A-18E/F aircraft.

Although the Royal Australian Air Force (RAAF) remains officially committed to the Lockheed Martin F-35, the Australian government plans to consider doubling the size of the Super Hornet fleet, signaled in a letter of request to the U.S. government. This is expected to raise fresh questions over Australia’s level of commitment to the F-35 and the final number of aircraft it will acquire.

Confirming the request in comments made to the Australian Broadcasting Corp., Defense Minister Stephen Smith says, “We placed a letter of request [LOR] with the United States authorities to enable us to investigate the potential purchase of up to 24 more Super Hornets.” Smith adds the F-35 “has been subject to very serious scheduling delays and that’s what’s causing us to risk a gap in capability…. We’re now looking not just to the Super Hornets [covering a] gap in capability, but whether into the longer term it makes sense for Australia to have a mixed fleet — a mixed fleet of Super Hornets, Growlers and Joint Strike Fighters, which is what you essentially see the United States Navy… embarking upon.”

The last of 24 Super Hornets was delivered to the RAAF by Boeing in late 2011. In early 2012, Australia announced a A$19 million contract for long-lead items to convert 12 of the newly-delivered F/A-18Fs into EA-18G Growler electronic attack aircraft. The decision was not unexpected, as the aircraft had earlier been provisioned for the Growler role on the Boeing production line in St. Louis under a separate A$35 million deal. It is not known if the next batch, if approved, will include additional Growlers or aircraft provisioned for modification for electronic attack, though the LOR is believed to cover a mix of both single-seat ‘E’ and two-seat ‘F’ versions.

Plans for the LOR, first revealed by the Australian Defense Department in December, came out of an Air Combat Capability Transition Plan conducted earlier in 2012. This studied the RAAF’s alternate options “in the light of Joint Strike Fighter project delays and the aging of Australia’s Classic F/A-18 Hornet fleet,” the department says in a statement.

“The Air Combat Capability Transition Plan considered the process for managing the RAAF’s transition from the current mix of Classic Hornet and Super Hornet to a future Air Combat Capability fleet, including the Joint Strike Fighter. The plan includes an assessment of progress of the Joint Strike Fighter project, the life of the existing 71 ‘Classic’ F/A-18 Hornets, any potential capability gap and management of the Super Hornet and Growler capabilities.” The statement adds that “the sending of this LOR does not commit Australia to purchase more Super Hornets. It is being sent so that the Australian government can further consider all options in 2013 with the latest and best cost and availability information.”

In his comments, Smith says the RAAF expects formally to take its first two F-35As from Lockheed Martin in 2014, though these will at first remain in the U.S. for initial pilot and ground crew training.

“We’ve announced that we will take another 12, effectively our first squadron, but we have not made a judgment as to when we will place the orders for those,” he adds. Assembly of the first center fuselage of the initial RAAF aircraft, AU-1, began in October 2012. The RAAF originally planned to purchase 100 F-35 jets for $16.4 billion, but delayed the order for the first batch of 12 aircraft by two years in May 2012 in light of Australian budget constraints.

Although the RAAF remains a staunch supporter of the baseline F/A-18, with some 71 aircraft currently in operation or undergoing life-extension upgrades, the option to acquire the Super Hornet was originally intended as a gap filler between the retirement of the F-111s in 2010 and the advent of the initial F-35s in late 2014. When the original RAAF F-35 order was placed in 2009, the service planned to activate the first full-up JSF squadron at RAAF Williamtown, New South Wales, in 2018.