First Appearance: LIAB Text 19
This is the first mention of "rangers," but it probably denotes a forest-capable (or possibly other terrain-specific?) scout.
Real World References
A nod to the Ford Ranger, a pickup truck produced by the Ford company. Also, would seem to bear a resemblance to former U.S. president Gerald Ford. He is shown in a uniform resembling that of a park ranger.
The line "I have not sought this enormous responsibility, but I will not shirk it." is taken from the speech Gerald Ford gave shortly after being sworn in as president after Nixon resigned.
In addition, it's been stated that Captain Ford and his forces were meant to be the occupying force at the captured Jetstone capital - in other words, its garrison. There is a famous actor named Harrison Ford, which sounds very similar to "garrison Ford".