Before the war, Israeli pilots and ground crews had trained extensively in rapid refitting of aircraft returning from sorties, enabling a single aircraft to sortie up to four times a day (as opposed to the norm in Arab air forces of one or two sorties per day). This enabled the Israeli Air Force (IAF) to send several attack waves against Egyptian airfields on the first day of the war, overwhelming the Egyptian Air Force, and allowed it to knock out other Arab air forces on the same day. This has contributed to the Arab belief that the IAF was helped by foreign air forces (see Controversies relating to the Six-Day War).