President Trump wanted one thing, more than anything else, from his secretary of the Navy, John Phelan: a new class of battleships.

“They’ll be the fastest, the biggest and by far — 100 times more powerful than any battleship ever built,” Mr. Trump boasted at a news conference at his Mar-a-Lago estate and resort in Florida a few days before Christmas. Mr. Phelan, a billionaire investor who has a home near the club, stood next to the president as he made the announcement.

Mr. Phelan’s job was to deliver the first of Mr. Trump’s battleships by 2028.

On Wednesday, Mr. Trump fired Mr. Phelan, who had struggled to come up with a plan to deliver the ships on the nearly impossible timeline that Mr. Trump has demanded, senior defense and administration officials said, speaking on the condition of anonymity to discuss sensitive personnel matters.....

Presidents rarely pay close attention to military procurement, but Mr. Trump has spoken repeatedly about his plans for a new “Trump-class” battleship. In a February speech to soldiers at Fort Bragg, N.C., Mr. Trump insisted that he had helped design the new class of ships that bear his name......

In Mr. Trump’s imagination the new warship would be massive, weighing as much as 40,000 tons, and would be packed with new high-tech weapons, like lasers, hypersonic missiles and electric rail guns, most of which are still in development and years from being deployed.

In recent weeks, it had become clear to Mr. Phelan that the Navy and the U.S. shipbuilding industry did not have the ability to deliver on Mr. Trump’s vision. Mr. Phelan recently suggested to Mr. Trump that the Navy might have to rely on European shipyards to deliver the battleships on the ambitious timeline Mr. Trump was demanding, senior military and administration officials said.

Mr. Trump rejected the suggestion.