Hi Amy,
I was a police cadet for 3 years at a state university pre-transition. I had no issues with it, aside from being forced to participate in the female-only self defense course that we were required to do. I probably could've avoided it if I had come out, but I wasn't ready to do that at the time.
After graduation I was hired by a major metropolitan police department on the east coast, and worked there for two years without transitioning. I enjoyed the job, didn't like the chief of police, and overall didn't think it was the right environment for me to transition in. Looking back now and seeing how progressive the department has gotten in the last few years since I've been out, I wish I had stayed in. I am considering asking to be reinstated after I have bottom surgery.