Donald Trump is ordering the US Navy to remove the system used to launch fighter jets from its newest type of aircraft carrier and return to using the older steam catapults that he has long said he prefers.According to a directive issued on Thursday, the mandate would likely cost billions of dollars and revert the navy's most advanced ships to a system that requires more sailors to operate and is more difficult to maintain.The memo directs the Pentagon and the navy to present Mr Trump with plans to remove the Electromagnetic Aircraft Launch System (EMALS) within two months.Donald Trump wants the US Navy to revert to old systems despite other world powers taking on the modern EMALS system. (US Navy: Seaman Daniel Kimmelman)It also says the Ford-class carrier's electromagnetic weapons elevators should be replaced.The move comes after years of Mr Trump railing against the new, magnetically powered catapult system that shoots fighter jets off the deck of the aircraft carriers.It also comes at a time when the US military is trying to find funding from congress for new equipment, while the navy struggles to fill its ships with enough sailors.Longstanding positionMr Trump's ire with the new technology goes back to at least 2017, when he claimed in a Time magazine during his first term that the new system was "not good" and "doesn't have the power" of the older, steam systems."You're going to goddamned steam," Mr Trump said at the time.The topic has frequently come up since then at rallies and other events.The newest Chinese aircraft carriers employ electromagnetic catapults, and France plans to use the system on its new carrier.Mr Trump's memo directs the fourth Ford-class carrier, the USS Doris Miller, to be the first ship to include the new changes. That will leave two ships untouched.'Careful reconsideration' neededEMALS manufacturer General Atomics says redesigning an already finalised ship for such a major system change will not be an easy task.The company told the Associated Press in an email that the decision not to proceed with the modern system on the USS Doris Miller "warrants careful reconsideration".Donald Trump and Pete Hegseth have prepared a $US95 billion package to fund the military. (AP Photo: Alex Brandon)General Atomics said the work on the USS Doris Miller's catapults and arresting gear was already halfway complete."Changing course now would introduce significant cost, schedule, and integration risks," it said.Re-budgeting requiredMr Trump's memo also noted that one of the issues facing shipbuilding was the navy's constant design changes, "which have resulted in cost growth, delays, and cancellations".The move comes as Congress is set to weigh the budget and funding bills that the Trump administration says it needs to fund the Pentagon and the Iran war.Defense Secretary Pete Hegseth estimated last month that the war's cost had grown to $US 37.5 billion as Republicans prepared a $US 95 billion package to fund the military, along with other White House priorities.US President Donald Trump speaks next to Defence Secretary Pete Hegseth (right). (Reuters: Evan Vucci)Mr Hegseth said the supplemental war funding was an "urgent, necessary" injection of money and represented, along with Trump's proposed $US 1.5 trillion defence budget, a generational investment in the military.The House narrowly adopted both but the Senate still must act when it returns in September.A key advantage to the electromagnetic system is the capability to launch aircraft at faster speeds while also being easier to maintain, requiring fewer sailors to operate and using less space aboard the ship.EMALS aboard the USS Ford cut the number of sailors need to operate the catapults from about a dozen to two.Reverting to a system that requires more people to operate it comes as the navy struggles to translate recruiting successes in the past year to actually filling jobs on warships. At the start of the year there were about 20,000 unfilled posts across the fleet.In February, the navy touted the system in a press release that said it allowed the USS Ford to launch and recover aircraft at a higher rate than its predecessor, the Nimitz-class ships.AP