Resolved questions
What's the meaning of this sentence?

Days passed. We came closer to our ship-out date, which was still being kept a secret by the higher-ups. But we felt it looming. The war had become a presence in our lives. We were grooms before a marriage. We trained in the snowy fields. We left the barracks in the morning, went to classrooms for briefings on the social structures and demographics of the unnamed towns that we’d be fighting for. We’d leave the classrooms at night with the sun already fallen as if by accident, somewhere to the west beyond the base’s barbwire fencing.
The last week we were in New Jersey, Sterling came to see us in our room. We were packing up all of our gear that we knew we wouldn’t need. The higher-ups had told us we’d have a pass soon and that our families would be able to see us for a last visit before our battalion’s movement. The only thing left was a final range day, put in place as the result of a suggestion Sergeant Sterling had passed up the chain of command. When Sterling stepped through our door, he waved off our somewhat lazy effort to rise to parade rest.
What's the meaning of " The only thing left was a final range day, put in place as the result of a suggestion Sergeant Sterling had passed up the chain of command."? What are the meanings of "range day" and "the chain of command"?
Thanks!