a routine trip or undertaking, especially one presenting little danger or difficulty:
The flight from New York to Chicago was a milk run for the experienced pilot and crew.
a routine and uneventful flight, esp on a dangerous mission
[C20: referring to the regular and safe routine of a milkman's round]
Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
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Then it examines the details of milk run operations, from truck selection to route planning.
Occasionally they send you on a milk run, which is an easy bombing run to start with, and get you kind of broken in.
But virtually they didn't concentrate much fire toward the airplanes so they were sort of called a milk run.
It was a milk run, lightly defended, with five ships around one dock in the port.