After World War II, the advent of jet aircraft necessitated a major reassessment of aviation maintenance, and flight jackets were no exception. One of the most significant changes in aviation equipment was the introduction of a hard helmet to protect pilots' heads from aircraft vibrations. However, the enlargement of the headgear interfered with the collar of the flight jackets. To address this issue, the "Modified" (MOD.) models were created in the B-15 series, with modifications made to the collar. This modification involved removing the shearling collar from the body and replacing it with a wool rib knit. In order to perform this alteration, the body had to be turned inside out, requiring the removal of the waistband rib. As a result, sewing marks can be seen on the collar and hem. This modification was commonly observed in the A, B, C, and D models of the B-15 series, and a white label was retroactively added to signify the official modification. It is often misunderstood that each type was developed and modified sequentially. In reality, the A, B, C, and D models of the outdated B-15 series were modified simultaneously according to the Technical Order issued in 1956.