The US Navy has contracted Boeing to deliver its final tranche of EA-18G Growlers, and the company is now looking to the Pentagon and abroad for more orders to sustain the common Growler and F/A-18E/F Super Hornet assembly line in St Louis beyond 2017.

The $898 million order for 15 aircraft, announced this week, rounds out the navy’s total requirement for 153 EA-18G advanced electronic attack jets – although Boeing says there are ongoing discussions and analysis with the navy about additional Growler and Super Hornet orders.

Boeing is in the process of cutting the output rate at St Louis from three aircraft per month to two by the first quarter of 2016 in an attempt to keep the line viable until at least 2019.

The need to secure future Super Hornet deals has gained more importance for Boeing in the light of Tuesday's selection of Northrop Grumman to build the US Air Force's Long-Range Strike Bomber. Unless Boeing wins the USAF's forthcoming T-X trainer contest, its future in combat aircraft manufacturing looks bleak.

Boeing confirms that the latest Growler order will sustain the line through 2017, and the company remains hopeful of another dozen Super Hornet orders from the Pentagon following budget deliberations in Congress. More commitments could also come from "a Middle East customer" – a package estimated at two-dozen or so aircraft.

In addition, a change of government in Canada last week could see Boeing compete to replace the Royal Canadian Air Force’s outdated CF-18s, if the new prime minister Justin Trudeau follows through with his promise to reject the Lockheed Martin F-35. Boeing is also awaiting an F-16 replacement decision from Denmark by the end of the year.

The F/A-18E/F is also a candidate to replace Finland’s 61 legacy C/D Hornets, where it is up against the Dassault Rafale, Eurofighter Typhoon, Lockheed Martin F-35 and Saab Gripen E.