Hi, Gibb. I've seen no contemporaneous evidence that "Shenandoah" began as a cavalry song or a soldier song or a "Civil War song." (The latter seems to be a favorite folkie idea recently - there really was a Shenandoah Valley during the Civil War, so obviously....),

The only "army connection" seems to be the verse that says, "He must have been a [number]th cavalry soldier after the line about the baby.

This strikes me as an obvious addition. Presumably one's own unit was specified, so as to humorously implicate (and flatter) oneself and fellow singers.

I've always felt the initial stress should come on "SHEN" after a lead-in "Ohhh!" But then, I've never worked a windlass.

I agree that it seems odd for sailors to sing about the "wild Missouri," which rises in Montana and flows into the Mississippi at St. Louis, far from the sea.

But "voyageurs" seem to me to be anachronistic.