Elon Musk is tearing into the F-35, the most expensive weapons program in history and a favorite of his new best friend, President-elect Donald Trump.

In a series of posts on X, the world’s richest man and proponent of driverless cars targeted the tri-service fighter jet program while coming out in favor of uncrewed aircraft.

“Manned fighter jets are obsolete in the age of drones,” he wrote on Monday. In another instance, Musk responded with the “100” emoji to another user’s tweet that “Drone superiority is the new air superiority.”

He also shared a video of Chinese drones and said “Meanwhile, some idiots are still building manned fighter jets like the F-35.”

The comments set up a potential rift between Musk and Trump, who spent the better part of his first presidential term touting his involvement in bringing the cost of the Lockheed Martin program down and then singing the praises of the fifth-generation stealth aircraft, saying in rallies that the plane is “invisible.”

Musk’s position as co-leader of a new advisory group meant to combat government inefficiency, however, means that defense producers are now looking to the tech billionaire for cues about government acquisition. The Department of Government Efficiency is tasked with helping the government reduce spending and cut regulations.

A spokesperson for Lockheed Martin, which produces the jet in partnership with Northrop Grumman and BAE, defended the F-35 as an advanced aircraft key to many operations, adding that the company looks forward to working with the Trump administration and the new Congress.

The F-35 program is the Defense Department’s most expensive program, topping out at a projected cost of $2 trillion, according to the U.S. Government Accountability Office, with more than $183 billion in cost-overruns.

While advocates have praised the plane’s capabilities, the rise of drones in Ukraine and elsewhere has prompted debate over whether the United States is investing enough in unmanned systems and other emerging tech that cost orders of magnitude less than typical Pentagon programs.

Those within the drone industry, meanwhile, warmed to Musk’s focus on autonomous systems.

“We’re a perfect fit for this new government,” said Jeff Thompson, CEO of Red Cat, whose subsidiary Teal recently won an Army competition to field thousands of small drones for the infantry.