In single-file the men marched through the communicating trench.
It was a single-file trail, and he walked in advance, silent as an Indian.
I understand that the arrival undiscovered was a result of riding in single-file and thus shewing no black mass.
The road now grew rougher, the guide leading and the rest following in single-file, Sylvia just ahead of Harley.
There was a steady, single-file procession of ants, with occasional gaps in the line.
Leaving the servants outside, single-file we trailed through the dark passage guarded by the wicketgate.
He clucked to his horse and the little cavalcade wound, single-file, up a narrow horse-trail toward the hills.
Passing out in single-file through the gate, they came upon Grey; but still they did not stop.
Beside the narrow board-walk over which the single-file line traveled, lay a circular affair of iron.
He made out a single-file column moving rapidly across a field, off the road.