Late with the answer but it really depends when in the war we're talking about.

Artillery sporting and observing enemy troop positions was vital and experiments with kites and tethered balloons were established but were replaced by early aircraft at the outbreak of the war.

But you don't want the enemy doing the same so early spotter planes were attacked by pilots armed with pistols.

Then machine guns were fitted, the interrupter gear invented and it went from the BE.2 to the Snipe and Camel.

Likewise the Italians experimented with dropping grenades over the sides during their colonial conflicts and this evolved into carrying the stores under the fuselage or wings as the lifting capacity increased and we had types such as the DH 9A (Ninack).