Lockheed RC-121D

Navigators on civilian airliners and long-range military aircraft, such as the Lockheed RC-121D, began using retractable periscopic sextants in the late 1940s. They eliminated the risk of astrodome blowouts in pressurized aircraft and produced less drag. But their narrow field of view made finding a particular star more difficult.

Caption:
This Lockheed RC-121D featured periscopic sextant ports for celestial sightings, eliminating the need for astrodomes.
Type: Photograph
Credit: National Air and Space Museum, Smithsonian Institution.
Origin: National Air and Space Museum, Smithsonian Institution.
NASM 83-6131
Navigation Methods
 
This Lockheed RC-121D featured periscopic sextant ports for celestial sightings, eliminating the need for astrodomes.