The first major strategic bombing campaigns were carried out during World War I. Initially by Zeppelin, and later by large bomber aircraft like the Gotha G.IV and Handley Page Type O, these raids were increasingly countered by fighter aircraft. This led to an obvious asymmetry; the attacking aircraft had to fly long distances to reach its target and thus had to be large enough to carry the required fuel load, while the defending fighters were flying only a short distance and therefore were able to be much lighter and have higher performance.