US Air Force Sergeant Luis Walker faces court-martial on Monday on multiple charges of rape and aggravated sexual assault of female recruits in his training squadron, the first of several such trials in the biggest military sex scandal in 16 years. Walker was one of roughly 500 Military Training Instructors at the Lackland Air Force Base in San Antonio, which conducts all of the Air Force\'s basic military training. If found guilty, Walker could face life in prison and dishonorable discharge. Since Walker\'s arrest 13 months ago, five more training instructors have been charged with raping or having inappropriate sexual relations with female trainees, or improperly fraternizing with them. Many are also facing lesser charges, including disobeying an order or adultery, which is a crime in the military. One of the six has pleaded guilty and told prosecutors he had inappropriate sexual relations with 10 women in his training squadron. A total of 31 women have come forward to say they were victims of improper sexual conduct, and six more instructors have been formally told they are under investigation. An additional 35 instructors have been removed from their positions pending investigation. The military has not seen such a large number of improper sexual conduct cases at one base since 1996, when a scandal at Aberdeen Proving Ground Army base in Maryland resulted in a dozen officers being charged with sexual assault. The Lackland scandal has sullied the reputation of the Air Force, where about one in five recruits are women, the highest of any military branch. \"This is taking away from what I\'m supposed to be doing, which is training airmen warriors to defend our country,\" said Lieutenant Colonel Tim Thurston, who commands a squadron conducting the 8-1/2-week basic training program at Lackland. \"It\'s going to take a little bit of time to regain that trust, and we understand that,\" he said. Female trainee Duree Purcell said the Air Force had gone out of its way to allow women to speak out about improper behavior. \"We have some bad MTIs, yes, but that\'s not how it is with the majority. There are steps to take so we can get out there if there is a problem and we can speak about it,\" she said. CHANGE TO BASIC TRAINING CONSIDERED Female cadets said the Air Force has placed anonymous complaint boxes in inconspicuous places in the barracks stairwells and has briefed them multiple times on the chain of command. \"It is frustrating for all of us,\" said Sarah Shaw, a trainee from Fayetteville, North Carolina. \"We came into the Air Force because we knew how high their integrity is. Now they\'re looking at us, and they think it\'s all scandal.\" Air Force officials said all 31 women who came forward to report inappropriate conduct were still in the service and stressed that some reports have not been substantiated so the accused trainer has been placed back on duty. The Air Force is considering drastic measures to deal with the scandal, including having female trainers in command of all-female units. About one in 10 training instructors is a woman. But most Air Force personnel interviewed on the base were opposed to the idea of single-sex training units. \"I would hate to live in an America where we said that women aren\'t capable of doing the same things that men do,\" Thurston said. \"There is absolutely no reason to think that women can\'t do every job, so why in the world would we make basic training separate for them.\" Thurston said his observation is that men do better with female instructors and women do better with male drill sergeants. \"Males don\'t want to embarrass themselves in front of a female instructor, and women look on a male MTI as somewhat of a father figure,\" he said. Colonel Eric Axelbank, commander of the 37th Flying Training Wing, said he was \"disappointed\" by the scandal but was doing all he could to deal with it. \"Within 72 hours of trainees getting here to Lackland, they know their values and they have been briefed on how to pursue allegations up the chain of command,\" he said. The scandal comes as the military is battling the problem of sexual assault in all the services, where women are playing increasing roles. A recent US Defense Department report said 4.4 percent of women in the military were the victims of unwanted sexual advances in the 12 months before the report. Women\'s rights groups believe the figure is far higher. Colonel Polly Kenney, the leader of the prosecution team in the courts-martial starting on Monday, said that as a woman she has never felt uncomfortable in her 23 years in the Air Force. \"As more and more cases came forward, we became more and more concerned,\" she said. \"It is unfortunate, but we have to deal with it.\"