Answer:
D. military encampment
Step-by-step explanation:
A bivouac is a type of shelter that is used as a temporary solution. This is particularly common with soldiers in the context of war, although it can also be used in other settings, such as while hiking or by scouts. In this example, we know that Bierce is describing an officer of the Federal Force and that he is in the context of war. Therefore, the phrase most closely resembles the meaning of military encampment.