Deuteronomy 1:15 (ESV)

15 So I took the heads of your tribes, wise and experienced men, and set them as heads over you, commanders of thousands, commanders of hundreds, commanders of fifties, commanders of tens, and officers, throughout your tribes.

Having obtained the peoples' cooperation, Moses then appointed the necessary leaders. He made them commanders, which underscores their authority in their units, and their function as military men. Those he made officers were likely less military than administrative leaders.