As early as the end of March, some Americans were leaving the city. Flights out of Saigon, lightly booked under ordinary circumstances, were full. Throughout April the speed of the evacuation increased, as the Defense Attaché Office (DAO) began to fly out nonessential personnel. Many Americans attached to the DAO refused to leave without their Vietnamese friends and dependents, who included common-law wives and children. It was illegal for the DAO to move these people to American soil, and this initially slowed down the rate of departure, but eventually the DAO began illegally flying undocumented Vietnamese to Clark Air Base in the Philippines.