Viljoen was the senior SADF military officer directing Operation Savannah in 1975. He is also credited with having planned the first major airborne assault in South African military history, Cassinga, a raid carried out against SWAPO insurgents. Despite his rank, Viljoen was present during the battle, offering what was described as a "swashbuckling" front-line leadership, which won him the respect of many fellow Afrikaners.