Don Barzini
Don Barzini thanked PJ Stein's answer

It is to avoid confusion between am and pm. Actually there are more countries that use a 24 hour clock than don't.  It is mostly countries that were or are under British rule that use the 12 hour clock. After being married to someone in the military, I found the 24 hour clock easier to … Read more

Don Barzini
Don Barzini thanked Yin And Yang's answer

And it keeps the concept of "24" hours straight with am and pm. For example if you say 1:00 is it 1:00 am or 1:00 pm? If you say 1300 hours then you KNOW it is 1:00pm. Also it's not just military. Nursing, doctors, cops, truckers, security, etc. Lots of people use military time.