Our cat is having a rough time adjusting to John being home. Any tips or suggestions to help him out?

just have him ignore the cat for a while. It will take a few days before the cat settles down especially all the smells coming from the ship that your dh brings home. Our dogs always get nervous when he is home at first because he smells different and they are used to certain things before he came home. Just like with kids, you gotta move slow with animals too.