SAN ANTONIO — From a chapel pulpit on Lackland Air Force Base, where every American airman reports for basic training, Colonel Glenn Palmer delivered his first order to nearly 600 recruits seated in the pews: If you’re sexually harassed or assaulted, tell someone.
‘‘My job is to give you a safe, effective training environment,’’ Palmer said firmly.
What the colonel did not mention directly in his recent address was a widening sex scandal that has rocked the base, one of the nation’s busiest military training centers. Allegations that male instructors had sex with — and in one case raped — female trainees have led to criminal charges against four men. Charges against others are possible.
The most serious accusations surround an Air Force staff sergeant scheduled to face a court-martial in July on charges that include rape and multiple counts of aggravated sexual assault. The other three defendants were charged with lesser crimes ranging from sexual misconduct to adultery.
All the defendants were assigned to turn recruits into airmen in eight weeks of basic training.
A two-star general is investigating in addition to a separate criminal inquiry, which military prosecutors say could implicate more airmen. Advocates for female service members and members of Congress have started taking notice.
‘‘It’s a pretty big scandal the Air Force is having to deal with at this point,’’ said Greg Jacob, a former Marine infantry officer and policy director of the Service Women’s Action Network. ‘‘It’s pretty substantial in its scope.’’
Yet there are signs the Air Force still does not have a handle on the full depth of the problem. Staff Sergeant Peter Vega-Maldonado pleaded guilty earlier this month to having sex with a female trainee and struck a plea deal for 90 days’ confinement. Then he acknowledged being involved with a total of 10 trainees, a number previously unknown to investigators.
On Friday, after months of embarrassing disclosures, the head of the Air Force’s training command ordered Major General Margaret H. Woodward to lead an independent investigation. That same day, the Air Force gave reporters rare access to Lackland’s instructional headquarters in an effort to show there was nothing to hide.
The headquarters facility is where Lackland trains the people who train recruits. Inside one small classroom, three women and two men were lectured on the importance of having a moral compass while watching a slide presentation titled ‘‘Integrity First.’’
Lackland has about 475 instructors for the nearly 36,000 airmen who will graduate this year. That is about 85 percent of what Lackland would consider a full roster of instructors. The job requires airmen to work longer hours than most for four years, at the expense of family and personal time.
The Air Force recently launched a smartphone app to help recruit instructors. Topping a page of frequently asked questions is whether the divorce rate for instructors really is higher. The Air Force says it is not.
Palmer said a slight shortage in instructors has not lowered the standards for applicants. In response to the allegations, he said instructor training is being revamped and that he was accountable for problems within the training wing.
Leaders of the instructor program, however, said the responsibility falls on the accused.
‘‘A person sitting in that seat, they’re going to do what they’re going to do when no one is watching,’’ said Master Sergeant Greg Pendleton, who oversees the training. ‘‘That’s across the board. That’s just them. When we’re outside this door or outside these walls, there are individuals that have their own personal values.’’
So widespread is the fallout that Lackland halted operations for an entire day in March to survey about 5,900 trainees about whether they had seen or been a victim of sexual misconduct.
The first sexual misconduct allegations at Lackland surfaced a year ago against Staff Sergeant Luis Walker, who is charged with 28 counts. Walker, the only instructor who has been accused of sexually assaulting another airman, faces life in prison if convicted.
Last week, one commander of a Lackland training squadron that was caught up in the sex scandal was dismissed after the Air Force lost confidence in his leadership. Officials said the dismissal was not directly related to the sexual misconduct investigation.