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The announcement immediately prompted questions on how the Trump administration intends to implement such a ban, how many people will be affected, and what will be the fate of transgender people already serving on active duty.
There are roughly 1,320 to 6,630 transgender service members on active duty, according to a RAND study published last year.
A 2014 study by The Williams Institute at the University of California, Los Angeles, pegs the number at closer to 15,500, including those on active duty or serving in the National Guard or Reserve forces.
The Williams Institute study estimates that there are 134,300 transgender veterans and retired Guard or Reserve service members.
The Pentagon has said it's unknown exactly how many transgender people serve in the military, as it only lifted its previous ban against transgender people serving openly in the military last July. Prior to that, transgender service members could have been discharged or denied reenlistment if they revealed their gender identities.
It remains unclear how the Trump administration plans to address openly transgender individuals already serving in the military, but the Pentagon announced Wednesday that it plans to defer enlistments by transgender applicants, NPR reported.
Brad Carson, a former Pentagon official who worked on transgender policy under the Obama administration, said the question had previously come up in discussions with the Joint Chiefs of Staff, according to Washington Post reporter Dan Lamothe.
"Every single" Joint Chief responded "no" when asked whether they wanted to oust transgender troops already serving competently, Carson said, according to Lamothe.