WWI - Forgotten Photographs

I'm just catching up on the BBC Four Hidden Histories program. I have this postcard amongst old family history photos which I know little about. I guess it's the Gloucester Regiment. It's taken in Cheltenham, probably on The Promenade. I have no idea if my grandad is on the photo. He signed up when he was 17. Or maybe my great uncles? But whenever I see a photo like this I think how young they look and of the many who never returned.