It was refered to as 'Shell Shock' (although that was something of a loose and/or variable term) and there are a number of posts about it in both wars and its link to mordern PTSD on here.

This one in particular.

In the WWI and WWII eras, understandings of PTSD were much more rudimentary. They weren't well-understood, either how they acted, or why they occurred. You see a bit of commentary about shell shock and battle fatigue, and you have mentions in contemporary literature of people having flashbacks, but such mentions lack the coherent ways these things are explained today. A few examples off the top of my head of places (outside of medical journals) where PTSD was referenced: in the mystery novel Whose Body?, published in 1923 and never out of print since that time, the main character suffers from flashbacks of trench warfare and he mentally goes away for a time. It's a detailed depiction of PTSD, something that at the time a large number of people would have seen happen and been familiar with when reading the book. But to a certain extent it was seen as embarrassing so it wasn't talked about as frankly as today. The novel Mrs. Dalloway was published in 1925, and one of the characters in it is suffering from PTSD and depression, and we follow him (and Mrs. Dalloway) during the last day of his life as he wrestles with his demons.

Then in the movie The Best Years of Our Lives, which won Best Picture Oscar of 1946, 3 American GIs are followed as they return from WWII. They all have problems with adjusting, PTSD, and depression, but it's all very muted as compared with, say, the post-Vietnam movies that talked about these things frankly. You can also look at the movie I'll Be Seeing You, from 1944, about a soldier with PTSD. These will all give you contemporary views. And wasn't there mention of a guy with "shell shock" in The Catcher in the Rye? As a WWII veteran, J.D. Salinger would have known a lot about that.