AN 5740 Master Navigation Chronometer

Many Army Air Forces navigators in World War II carried a chronometer set to Greenwich Civil Time (later Greenwich Mean Time) and mounted in a special hardened case with shock absorbing springs. 

Caption:
One of the most common navigation watches produced, with many used by the U.S. military well into the Cold War era.
Type: Artifact
Image Date: 2012
Credit: National Air and Space Museum, Smithsonian Institution
Origin: National Air and Space Museum, Smithsonian Institution
Creator: Eric Long
NASM2012-02164
Innovations
Navigation Methods
 
One of the most common navigation watches produced, with many used by the U.S. military well into the Cold War era.
One of the most common navigation watches produced, with many used by the U.S. military well into the Cold War era.