The first version of the tandem-rotor military helicopter CH-47 Chinook could lift more than seven tons. The CH-47SD International Chinook, launched in 1998, lifts twice as much. At peak production in 1967, the Boeing Vertol Philadelphia plant produced a new Chinook every 24 hours, and by 2002, the Chinook’s high speed and large payload gave it the lowest cost-per-ton-mile of any transport helicopter available. The Model 234 is a commercial derivative of the Chinook, and U.S. Army Special Operations Forces also operate Special Operations Chinooks, designated as MH-47Ds and MH-47Es. The MH-47Es are among the most advanced rotorcraft in operation today. Special Operations Chinooks perform low-level, high-speed flights at night and in adverse weather.