|World War 2 teletype|
The practice is probably pretty out of date, given that young sailors are texting, using social media, and, well, working far beyond the teletype technology that began the all caps requirement.
In addition, typographers maintain that text in all caps is harder to read. People tend to recognize whole words, along with letters' ascenders and descenders, as opposed to reading every letter.
Check out the story at:
- the Wall Street Journal.
- PC Magazine.