GR translation: Military working parties go at route-step bitching in and out

[Mike Jing]

P308.30-37   Post-A4 humanity is moving, hammering, and shouting among the
tunnels. Slothrop will catch sight of badged civilians in khaki, helmet
liners with GE stenciled on, sometimes getting a nod, eyeglasses flashing
under a distant light bulb, most often ignored. Military working parties go
at route-step bitching in and out, carrying crates. Slothrop is hungry and
Yellow James is nowhere in sight. But there is nobody down here even going
to say howdy to, much less feed, the free lance Ian Scuffling.

Does "bitching" mean "complaining" here?  I assume "in and out" refers to
the "route-step".
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