The XF8U-3 first flew on 2 June 1958. Despite claims by many books and articles that the aircraft reached Mach 2.6 at 35,000 ft (10,670 m) during testing, the maximum speed achieved was Mach 2.39, and normal operating speed was no more than Mach 2.32. The first time that the aircraft exceeded Mach 2.0 in level flight was on August 14, during its 38th test flight, well before the rival F4H-1 did so. Some sources state that Vought projected a top speed of Mach 2.9 with the tail rocket installed, though the windscreen and most aluminum airframes were not designed to withstand the heat of speeds more than Mach 2.35. Demonstrated zoom ceiling was well over 76,000 ft (23,170 m). In December 1955, the US Navy declared a competition for a Mach 2+ fleet defense interceptor. Fly-offs against the Crusader III's main competitor, the future McDonnell Douglas F-4 Phantom II, demonstrated that the Vought design had a definite advantage in maneuverability. John Konrad, Vought's chief test pilot, later stated that the Crusader III could fly circles around the Phantom II. Combat thrust-to-weight ratio (T/W ratio) was almost unity (0.97), while early F4H was only at 0.87. However, the solitary pilot in the XF8U-3 was easily overwhelmed with the workload required to fly the intercept and fire Sparrows which required constant radar illumination from the firing aircraft, while the Phantom II had a dedicated radar intercept officer on board.