Washington (CNN) President Donald Trump used a term from US segregationist history to describe the relationship between the Air Force and his newest military branch, the Space Force, calling it "separate but equal."

"We must have American dominance in space. Very importantly, I'm hereby directing the Department of Defense and Pentagon to immediately begin the process necessary to establish the Space Force as the sixth branch of the armed forces. That's a big step," he said in the White House East Room during a meeting of his National Space Council Monday.

"We are going to have the Air Force and we are going to have the Space Force: separate but equal, it is going to be something so important," he said.

The term "separate but equal" became a legal precedent following an 1896 Supreme Court ruling Plessy v. Ferguson that said the use of racially separate facilities, if equal, was not discrimination. That legal rationale was deemed unconstitutional through a series of Supreme Court decisions, ending with 1954's Brown v. Board of Education.

In addition to calling for the Space Force, Trump signed Space Policy Directive -- 3 on Monday, part of his administration's push to lead in the space space.

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