 In three years of activity de Greef aided 101 exfiltration missions which successfully exfiltrated 288 airmen, mainly British and American, and 84 other persons, mostly Belgians, needing to escape occupied Europe.The allies put a high priority on recovering airmen shot down in Europe and returning them to service as it was time-consuming and expensive to train replacement aircrew.De Greef also supervised the finances of the southern section, accounting for the expenditure of 17 million French Francs (equivalent to 5 million in 2017 U.S. dollars).