Complex sentence: Initially, these aircraft were to be given USAAC serials 39-618 to 39-687 however, delays with the actual purchase the serials numbers were changed to 40-696 to 40-702.
Split into simpler sentences: Initially, these aircraft were to be given USAAC serials 39-618 to 39-687. Due to delays with the actual purchase, however, the serial numbers were changed to 40-696 to 40-702.