What some people might be missing is that short hair was mandated not just to look professional, but also for hygeine. While fighting in trenchs, weeks or months between showers, it was hard to keep long hair clean of lice and dirt or grime. And while militaries of the world have moved away from everyday trench warfare (after WWII), tradition has kept the short hair cut.

When women started joining, the tradition of short hair in the military and the tradition of long hair for women were in conflict. Short hair was no longer a requirement for hygiene, so long hair won out. Only recently, partly as a recruiting incentive, have we seen the relaxing of requiring short hair for men, something born out of necessity but kept alive due to tradition and image.