Depending on your definition of "need". Categorical imperative, no.
Personal experience, I did not have a Masters but I did have a bachelors in electrical engineering, with bit of 12 years TIS and 29 years old when promoted to Master Chief. That was some time ago, long before there were "on-line" degrees. I was fortunate to have 4 years continuous shore duty in WashDC enabling completion of my degree in a field directly related to my rating. Am sure that looked impressive to the board, and I base that statement on end result.