Originally reconnaissance.
No jet aircraft were used in WW1.
14.3
aircraft, tanks, dreadnoughts,
Both sides used aircraft, early in the war, as reconnaissance. When the war started each side had a small number of aircraft on hand, so they were used almost from the beginning.
ENGLAND
world war one aircraft were simply built to carry out their missions while aircraft of the golden age were built for comfort.
Aircraft were used all through WW1. Both sides started off with unarmed spotter aircraft for ranging artillery and soon progressed to genuine fighters and eventually bombers.
Spad 13
World War 1 saw the introduction of the tank and of aircraft.
Tanks, aircraft, poison gas and the Dreadnought Battleship
A Farewell to Arms is a good book reference to know the that aircraft log book was practiced in World War 1.
Dozens of different aircraft were developed and used in WW1. There wasn't a single airplane type.