Judging from the shape of my dad's hat, it would appear that certain non-flying personnel were authorized to remove the retaining band and wear the "crusher" style that was all the rage among air crews of the era. The practical purpose for removing the retaining band was to allow earphones to fit more comfortably over the head during flight operations. The "crusher" was also useful in attracting the attention of female patrons of Officer's and NCO Clubs.