Better known by its commercial designation Bell 47, the H-13 Sioux was the first helicopter in service with the US Army and the first helicopter in the world certified for general use. The H-13 was easily recognized by its full bubble canopy, exposed tail boom and landing skids. It was used primarily for observation but also used for training. Despite these being its primary missions, the most memorable use of the H-13 was that as a medical evacuation helicopter, fitted with panniers attached to each skid. These MASH (Mobile Army Surgical Hospital) units saw extensive service during the Korean War and were immortalized in the long-running series of the same name. The H-13 remained in service during the early years of the Vietnam War until eventually replaced by the OH-6. H-13s were in service with dozens of countries including many NATO allies and were license-produced in Japan, Italy and the UK. Some remained in service into the 21st century and many commercial Bell 47s are also in use today.

The first prototype of the Bell 47 flew on 8 December 1945 and first orders for the US Army came in 1946 as the YH-13 followed by the production H-13B. Further modifications resulted in the H-13C with external stretchers, skid landing gear plus a new engine in the H-13D. A three-seater version was known as the OH-13E and was the most widely built variant. Other observation variants based on the upgraded commercial 47G were the OH-6G, OH-6H (with a new Lycoming engine) and the OH-13S. Utility variants used by the US Navy were designated HTL. A dedicated trainer variant was the TH-13T while a pair of presidential transports were known as the UH-13J. British units were known as the Sioux AH.1 of which some were built by Agusta before production switched to Westland (a trainer variant was the HT.1). A Japanese variant was the KH-4 license-built by Kawasaki and featured an enlarged cabin.