This is a Navy term used for sailors below the rank of E7. It comes from the color of jacket worn by those sailors, which happens to be Navy blue. All other sailors ranked E7 and above wear khaki colored clothing and jackets.

The Navy also has a manual called “The Bluejacket Manual.” This has all the information needed by an enlisted sailor to get along in the Navy. Every new recruit gets a copy of the Bluejacket manual when they enter the Navy and are expected to know what is inside. My recruiter gave me a copy when I had officially enlisted. He said read it, know it, live it. (Sorry stole that from Fast Times)

There is historical information about the Navy and everyday things a sailor needs to know. Orlando RTC had a small ship that was called the Bluejacket. This was a trainer where we learned different Navy lessons. After boot camp those who entered apprentice training spent more time onboard the Bluejacket learning basic seamanship.

Being an E6 and below sailor even your working jacket is blue. The P-coat, rain coat, and even your wind breaker are all blue. Your winter dress uniform and working uniform are both blue. Even your day to day working uniform is also blue. So, calling those people blue jackets only makes sense.

Even officers read the Blue Jacket Manual to learn basic Naval rules. Many people onboard my ship collected old copies of the Blue jacket Manual. Some of the information was very interesting. One of our warrant officers had a copy from the early 1900’s. He would use that when we would play “Stump the Chump” during the midwatch with the bridge.