SAN ANTONIO — After her Air Force training instructor raped Virginia Messick, a young recruit, he told her it was fun and they should do it again, she remembers. Then he threw her clothes at her and ordered her to take a shower.

Ms. Messick was unable to move, cry or scream. She was a 19-year-old from rural Florida, in her fifth week of basic training at Lackland Air Force Base, and she had just been assaulted by the man the Air Force had entrusted with her life.

After the April 2011 attack, Ms. Messick completed basic training, following orders from the instructor for nearly a month more. Afraid of the consequences, she did not tell anyone what he had done. “How am I supposed to go about reporting something,” asked Ms. Messick, “when the person I’m supposed to report to is the person who raped me?”

Now, after leaving the Air Force, Ms. Messick is the first victim of a still-unfolding sexual assault scandal at Lackland to speak publicly about what she has endured. Since accounts of sexual violence at the base began to surface in late 2011, it has emerged as the largest such episode in Air Force history.