In this chapter, war is a reality in the boys' lives, and that reality comes home, literally, as troops move onto their campus. In a war, there are so many different branches, divisions, and areas that are necessary to function well; behind the scenes of the battles and the front is an army of messengers, communications, mechanics, and other technical and mechanical necessities. The division that gets put onto the Devon campus belongs to "The Parachute Riggers," or the division of the war that takes care of making parachutes for all of the troops that are dropped into war zones from planes. They also train troops on how to use the parachutes correctly.
The first thing that Gene and Brinker notice is that the entire division hauls in what appears to be sewing machines. It's not the first thing that you think of when you see troops, or think of war, but, as Gene puts it,
"I guess a Parachute Riggers' school has to have sewing machines."
Someone has to sew the large swaths of fabric together to make the parachutes, and use the machines to patch and repair any damages to the chutes. With the machines come the troops, the drill sergeants, the war songs that the troops sing, the Jeeps and machines of war. They look out their window and literally see the implements of war at their doorstep. The war is no longer an ambivalent, distant force that might influence their lives, it is a reality, and it will, in the end, impact all of their lives in one way or another.
I hope that those thoughts helped; good luck!