And? One loud noise can diminish temporarily or permanently a persons hearing. Repeated loud noises can diminish a person's hearing over time, as a gradual "over time" loss, which if that is the case, "over time" testing would reveal such. And simply old age can diminish hearing.
Simply saying, he was in the artillery, doesn't provide any facts per the state of his hearing.
Ahhh, speak up. As for the VA, I hate that bureaucracy with a passion.