Sometimes rules regarding capitalization are controversial and can be debated. For instance, take military terms. Should writers capitalize Navy, or should navy be lowercased? Should Army be capitalized, or should army be lowercased?
According to The Chicago Manual of Style, if we’re spelling out the full name of a particular army or navy, it’s capitalized. If the word army, navy, air force and so on stands alone, then those words are lowercased.
Example: Army of the Potomac, United States Army, United States Navy, the army, Union navy, etc.
Not every stylebook agrees with this, though they all agree these words should be capitalized when spelling out the full name of a specific branch of the armed services.
The Associated Press Stylebook takes a different view from The Chicago Manual of Style. It says to capitalize the abbreviated form of military branches: Navy, Army, Air Force, Coast Guard, Marines. So does the Government Printing Office (GPO).
Another case is how to spell marine. Is it capitalized, or is it not? I’ve seen it spelled both ways by well-respected historians, just as I’ve seen Confederate Navy and Confederate navy in excellent history books.
The New York Times used to spell marine in the lowercase so it’d be the same as soldier and sailor, as the newspaper explained. According to a recent report the paper has changed its style requirements to start spelling it in the uppercase, even when referring to an individual Marine. The Navy’s style manual agrees with this.
This debate will likely never end because style manuals differ. The one rule that doesn’t change is this: when referring to the full name of a national army, navy, air force, coast guard, marines—always capitalize. Whatever style manual we use in other cases, keep our style consistent throughout our work.