I've read that by the end of World War I they had both contact and timed fuses(fuzes?), so in the case of a timed fuse (early in the war?), the bomb would just explode early, but what of the contact ...
I know for a fact that aeroplanes were used at the last stages of the first world war to capture images of the enemy trench system and supply lines. They were also used to alert the artillery how far ...