You don't need anything. This is " to be to" structure. It works pretty much like "have to". We usually use it with scheduled events.

There are many possible words you could use: ordered, commanded, instructed, supposed, required etc. Not “sure”. “needed” would be grammatically ok but would change the meaning. Leaving it out is more succinct. The commander is telling him what to do and doesn’t need to explain.

The example has a grammar error: "THE civilians" or "ALL civilians" is required. Also, "evacuate" is a more natural word than "relocate." New Oxford American Dictionary: evacuate - verb remove (someone) from a place of danger to a safe place: several families were evacuated from their homes. ---------- The structure (I am/You are/He is/She is/We are/They are - to do) is one way to express obligation, although it is not common in North America. https://www.ef.com/ca/english-resources/english-grammar/future/ [excerpt[ "Obligation: You are to travel directly to London." -------- For natural wording, the officer has one good choice (the imperative): "Sargeant, Evacuate the civilians!" For an English exercise using this structure, the officer could say: "Sargeant, We have received new orders. We are to evacuate the civilians." More natural in North America is "Sargeant, We have received new orders. We must evacuate the civilians."