Historically, these investigations have been handled by the higher-ups in the chain of command. Say one soldier raped another and the victim reported it. Their mutual boss and that boss's bosses would be responsible for any investigation and discipline.
They have the same negative incentive to provide thorough investigation and justice as college campus police do - because in the end it makes them look bad at their jobs and makes the institution that signs their paychecks look bad. So they just don't. Often victims are ignored or worse, disciplined themselves.
This change will provide a third party not involved in the chain of command for reporting and investigation of sexual assault allegations.