Need help with mixed trains

Hey, I'm a novice model railroader, but I recently decided to build a GWR coach because I love the brown and cream color combination. But now that I have my coach, I would like to develop it. Was it possible for a train to pull coaches and wagons/van in the 1930s/ww2 ? And did the trains undergo any specific modifications during the war? (Movement of soldiers, equipment, etc.)? Sorry if the question is dumb but I'm getting lost on internet and can't find a definitive answer submitted by ...