Complex sentence: In the early stages of the Vietnam War he authored a report in which he predicted the Vietcong would make use of the intercoastal waterways and rivers, while initially dismissed it was later used as a source to increase the use of Navy SEALs in direct action missions.
Split into simpler sentences: In the early stages of the Vietnam War he authored a report in which he predicted the Vietcong would make use of the intercoastal waterways and rivers. While initially dismissed this report was later used as a source to increase the use of Navy SEALs in direct action missions.