With all the women now in the military, hair lengths for men should be relaxed. I recall my black soldiers with beards after they were diagnosed with pseudofolliculitis. Funny though, I never saw a black officer or senior NCO with a beard.
I knew several senior black (and at least one white) NCOs and officers over my career with this condition. They generally kept it trimmed to around 1/8", dependent upon their profile.
That condition (for those who don't know, its where short curly hair stubble curls around and grows into the skin) is extremely painful, I never begrudged anyone with a legitimate profile for this condition.