Semi annual. When I was in, we had to weigh in every time. Some made weight, but they had too much body fat. That should have resulted in remedial PT, and if you have three strikes on that, you're out. However, it depends on how high you are to determine how difficult it would be to kick you out of the military just for being fat. Fatasses shouldn't be on ships because the vertical hatches are supposed to support you and an SCBA (oxygen tank used for fire fighting).