Another early shot of the first prototype Bell HSL, most probably during its maiden flight at Amon Carter Field. The only tandem rotor helicopter attempted by Bell, the HSL was almost too big for aircraft carrier elevators and high noise and vibration levels interfered with sonar work in the intended ASW role. A few airframes used in minesweeping trials. Photo from: Bell

Built to an urgent requirement for an anti-submarine warfare helicopter, the Bell 61, US Navy designation HSL, was a failure that never went into operational service although 53 airframes were completed. The photo shows the first prototype on its maiden flight, which took place at then Amon Carter Field. That site opened for passengers as the short-lived Greater Southwest International Airport one month later. Photo from: Bell