|National origin||United States|
|Primary user||Peruvian Navy|
The Keystone K-55 Pronto was a mail plane developed in the United States in the late 1920s. It was a conventional single-bay, unequal-span biplane design with slightly staggered wings. The pilot sat in an open cockpit, in tandem with a second cockpit that could carry two passengers side-by-side. The fixed, tailskid undercarriage had divided main units.
A number of these aircraft were purchased by the government of Peru. Operated by the aviation arm of the Peruvian Navy, these aircraft initiated the first airmail service into the Peruvian Amazon. The first flight of this service was made by two Prontos, piloted by Leonardo Alvariño Herr and Harold B. Grow from Lima to San Ramón on 26 October 1927.
At least one Peruvian Pronto was fitted with pontoons and used to survey the Amazon River for locations suitable for seaplane operations.
In the Colombia-Peru War one Peruvian K-55 flow by Lieutenant Suero was captured by the Colombian Army.
- Crew: One pilot
- Capacity: 2 passengers
- Length: 26 ft 9 in (8.15 m)
- Wingspan: 39 ft 11 in (12.17 m)
- Powerplant: 1 × Wright J-5, 220 hp (160 kW)
- Maximum speed: 112 mph (180 km/h)
- Range: 500 miles (800 km)
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- Taylor, Michael J. H. (1989). Jane's Encyclopedia of Aviation. London: Studio Editions. p. 560.