PreCheck is free for active US military and requires no application with DHS/TSA for that.
GE requires an application, getting CBP to conditionally approve the person and then an interview for the usual purposes applicable to all conditionally-approved applicants. Given credit/charge card fee waivers applicable to US military personnel, there is the path of getting a bank card that reimburses the GE application fee. And then doing the interview as part of the GE enrollment on arrival process for those conditionally approved. No interview booking needed as long as completing the process within 12 months of conditional approval.