The Hiller H-23 Raven Light Observation Helicopter was based on the Hiller-produced U.S. Navy UH-12, which was first flown in 1948. The H-23 Raven performed as a utility, observation, and MedEvac helicopter during the Korean war. Model numbers ranged A through D, F and G (no model E was procured).
H-23 Raven Models A, B, C, D and G were 3-place while the H-23F was 4-place. The H-23F had a 25 inch cabin extension which placed the pilot in front of the the three original positions. Only 33 of the F-models were procured by the U.S. Army.
The Hiller H-23A Raven Helicopter had a sloping front windshield. The H-23B was used as a primary helicopter trainer. Beginning with the UH-23C, all later models featured the "Goldfish bowl" canopy similar to the Bell H-13 Sioux helicopter. The H-23 Raven also featured the Hiller "Rotomatic" system -- two paddles at right angles to the two rotor blades -- that produced great stability and insulated the pilot from rotor vibrations.
The OH-23D was a purely military version with a O-435-23C engine and a more reliable transmission. Most OH-23Ds were replaced by the OH-23G, the most common version of the Raven, with a more powerful Lycoming O-540-9A six-cylinder, horizontally opposed, air cooled 305 hp engine. The MedEvac version carried two external skid-mounted litters or pods.
The U.S. Navy procured the same helicopter under the designation HTE-1 (similar to Army H-23A, but with four wheels instead of three) and HTE-2 (similar to Army H-23B, but with four wheels instead of skids.)
The Hiller OH-23 Raven served during the early part of the Vietnam war but was replaced by the OH-6A Cayuse in early 1968.