U.S. President Donald Trump is on his way back to the United States after a four-day visit to Japan, but didn't leave before explaining how the redesign of U.S. aircraft carriers is wrong.

During his stay, he met Japan’s new emperor and held serious discussions with Prime Minister Shinzo Abe about North Korea, Iran and trade. He and Abe also played golf and attended a sumo wrestling match.

On Tuesday, Trump and first lady Melania Trump went aboard a Japanese destroyer to visit Japanese troops and then made a visit to the USS Wasp docked at the mouth of Tokyo Bay. Aboard the USS Wasp, Trump gave a Memorial Day speech to hundreds of members of the U.S. Navy’s 7th Fleet.

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Trump spoke while aboard the ship and offered his thoughts on aircraft carrier design. "You know, they were saying — one of the folks said, 'No, the electric works faster. But, sir, we can only get the plane there every couple of minutes,'" Trump said according to a White House transcript. "So, really, what they did was wrong."

"I think I’m going to put an order," the president continued. "When we build a new aircraft carrier, we’re going to use steam. I’m going to just put out an order: We’re going to use steam. We don’t need — we don’t need that extra speed."

“Steam’s only worked for about 65 years perfectly,” Trump continued.

“And I won’t tell you this because it’s before my time by a little bit, but they have a $900 million cost overrun on this crazy electric catapult," Trump said.