From a 2017 armytimes.com article on trans in the military:
The most expensive and involved part of transition would be genital reassignment surgery, which most transgender people do not undergo.
Much more common are cosmetic surgeries like breast implants or reductions, as well as facial surgeries, that are not covered by DoD.
I know this will be unpopular here, but I only care if he-she-it-whatever, can do he-she-it’s job.