Dr. Rachel Levine is the nation’s first openly transgender four-star admiral.

Levine, the assistant secretary of health, was sworn in on Tuesday.

She is now the highest-ranking official of the U.S. Public Health Service Commissioned Corps.

“I am deeply honored and grateful to join the ranks of men and women across this great nation who have committed to defend the United States against small and large threats, known and unknown,” Levine said. “I promise to uphold that trust to the fullest extent of my abilities.”

Levine acknowledged the historic nature of her appointment.

"I stand on the shoulders of those LGBTQ+ individuals who came before me, both those known and unknown. May this appointment today be the first of many more to come, as we create a diverse and more inclusive future."

The Commissioned Corps serve in various health care roles around the world to protect public health.

Levine will oversee 6,000 officers in her new position.