When I was stationed in Korea ('93-'95), the term "turtle" was used to describe the recently arrived GI's. It was also yelled in the mess hall when somebody dropped a tray, tripped, etc. The term was used frequently by every soldier throughout Korea.
The origin is said to come from the observation that the in-processing building and the out-processing building are close to each other but takes a turtles' pace (or one year) to travel between them. It's a convincing story but was always told with a grain of salt.

So what's the origin of "turtle" as used by the GI's stationed Korea?

P.S. – I love your podcasts.