Replace the question mark with a number

A young lad was visiting a church for the first time, checking all the announcements and posters along the walls.
When he came to a group of pictures of men in uniform, he asked a nearby usher, "Who are all those men in the pictures?"
The usher replied, "Why, those are our boys who died in the service".
Dumbfounded, the youngster asked, "Was that the morning service or the evening service?"