Lockheed H-51

The Lockheed H‑51, originally designated the OH‑23 Raven, was a light observation helicopter that entered service with the United States Army in 1949. Developed from the earlier XR‑4 prototype, the H‑51 was built by Lockheed Corporation under a joint venture with Sikorsky, and it became one of the first rotorcraft to be produced in large numbers for military use. Powered by a 180‑horsepower Lycoming O‑435-3 engine, the helicopter featured a two‑bladed main rotor, a simple fixed‑pitch tail rotor, and an all‑metal tubular frame that gave it durability in harsh field conditions. Its modest payload capacity allowed a pilot and an observer, plus a limited cargo load, making it ideal for artillery spotting, liaison, and medical evacuation missions during the Korean War and early Vietnam conflict. The H‑51’s easy maintenance, low operating cost, and straightforward controls set a benchmark for subsequent utility helicopters. Its widespread adoption by over 30 nations helped standardize rotary‑wing tactics worldwide, and the aircraft’s legacy can be seen in the design philosophy of later Lockheed‑Sikorsky models such as the UH‑60 Black Hawk. Today, a few restored H‑51s still fly at airshows, serving as living reminders of the helicopter’s pioneering role in modern warfare.