Resolved questions
What's the meaning of this sentence?

It is military terminology. The word "rank" has many meanings. One meaning of "rank" is a line of soldiers standing side by side in an orderly arrangement. The orderly arrangement is called a "formation." A closed rank is when the soldiers stand close to each other. An open rank is when there is a small but noticeable distance between them. So Murph pivoted (turned around right where he was located) and moved through (walked through) the open rank of the formation (the orderly line of soldiers who were standing a bit apart from each other).