President Trump had wanted an independent Space Force Department. (Evan Vucci/AP)

President Trump signed a policy directive Tuesday that laid out a framework for the Space Force he has long sought, but the plan falls short of his initial vision for a new service that is “separate but equal” to the Air Force.

In the document, the president directed the Pentagon to create legislation for Congress that would place the Space Force under the control of the Air Force Department, in a fashion similar to how the Navy Department oversees the Marine Corps. It marks a partial win for senior Air Force officials, who had argued that creating a separate military department — as Trump had stated he wanted — would create unnecessary Pentagon bureaucracy.

Trump signed the directive Tuesday afternoon in the Oval Office while flanked by senior defense officials that included acting defense secretary Patrick Shanahan, Air Force Secretary Heather Wilson and Air Force Gen. Paul Selva, the vice chairman of the Joint Chiefs of Staff. The president said he was “thrilled” to do so, and believes it is just the beginning of an important process.

“Our adversaries ... whether we get along with them or not, they’re up in space,” Trump said. “And they’re doing it, and we’re doing it. And that’s going to be a very big part of where the defense of our nation — and you could say ‘offense,’ but let’s just be nice about it and let’s say the defense of our nation — is going to be.”

The plan, which requires congressional approval, could mark the first time the U.S. government has established a new military branch since the National Security Act of 1947 created the Air Force in the wake of World War II. The administration could press for a full Space Force Department in the future, but it is unclear whether or when that would happen.

The move appears to mark a rhetorical and political compromise: While the Trump administration will continue to call the new service the Space Force, it will more closely resemble a previous proposal on Capitol Hill for a smaller Space Corps that does not have a new, separate service secretary appointed by the president. Like the Marine Corps, it will be led by a four-star general who takes a new seat among the Joint Chiefs of Staff, the Pentagon’s top officers.

A Pentagon spokesman, Charles E. Summers Jr., said that in coming weeks the Defense Department will submit a legislative proposal to Congress that authorizes the establishment of the Space Force as the sixth branch of the U.S. military.

“The United States considers freedom to operate in space a vital national interest, one that is fundamental to our prosperity and security,” Summers said. “With Space Policy Directive-4, President Trump is posturing the United States to compete, deter and win in a complex multi-domain environment characterized by great power competition.”

Gen. David L. Goldfein, chief of staff of the Air Force, said Tuesday morning that U.S. officials examined options ranging from the creation of a full space department that would have had its own service secretary to something akin to the Medical Corps, a part of the U.S. Army comprising medical professionals in uniform.

“We wanted a robust debate, as you would imagine, on where was the right place to land that aligns with the president’s direction, and what’s going to roll out today is a service within the Department of the Air Force,” Goldfein said during a public appearance at the Brookings Institution in Washington.

Shanahan was expected to sign a memo directing Wilson to establish a team to finalize details of the Pentagon’s space plan, Defense One reported last week, citing a draft memo. The Pentagon also will create a Space Force undersecretary who reports to Wilson and a four-star vice chief of staff who reports to the Space Force service chief, the report said.

Trump created a new position, chief of U.S. Space Command, in December. The four-star officer will oversee the U.S. military’s operations in space, which are currently focused on communications, surveillance and defending U.S. satellites from threats posed both by the elements and by adversaries such as Russia and China.

Goldfein said Tuesday that he sees the creation of the head of Space Command as the most important step. It will allow the services to prepare troops for the Space Command chief to use, he said, similar to how the services prepare troops to be deployed under the control of U.S. Special Operations Command.

“I think the fact that we’re having a national debate on space is really healthy. Really healthy,” Goldfein said. " . . . We’re the best in the world at space, and our adversaries know it, and they’ve been studying us and investing in ways to take away that capability in crisis or conflict. That, to me, is the problem statement, and we as a nation cannot let that happen.”