The bluff worked, largely thanks to the dog, who turned out to be friendliness incarnate and quickly won over the MPs and the commanding officer of Donovan's unit, who promptly made Rags' mascot status official. Rags enjoyed his new gig thoroughly and thanked his new human friends the only way a dog can -- with googly eyes, a wagging tail and impromptu face-licking attacks. Also, by saving everyone's lives on a daily basis and becoming one of the unit's greatest heroes.
When Donovan was transferred to the frontline, he didn't want to risk Rags' life, so he left the little guy behind. The dog, however, wasn't having any of it, and tracked Donovan to the trenches. Realizing that the pup was good at finding his way around, Donovan adapted a secondary strategy: He taught Rags how to run messages between the command and the frontline.
"We'll just ... tuck this into your collar, shall we?"
Rags took his promotion incredibly well, regularly delivering important messages despite constant gunfire, explosions, distracting smells and other stuff custom made to lead a dog astray. He wasn't just doing his part, either -- he constantly watched and studied the things the soldiers around him did. When the men hit the dirt upon hearing a shell, Rags would mime their actions.