Airships were falling out of favour with militaries even during WWI, as improved aircraft capabilities and the inherent weaknesses of airships made themselves clear. Zeppelins were useful for strategic bombing in the early part of WWI, as they were just as fast as the available aircraft, had a higher payload, and could fly higher and further. They could outrun or outclimb any aircraft that tried to shoot them down. In many cases, Zeppelins were able to simply fly higher than the aircraft that tried to intercept them. The German Navy and Army saw reasonable success using them against British towns and cities in 1914-1916. However, the war saw considerable improvements in the abilities of aircraft, and by September 1916, aircraft that could intercept and destroy Zeppelins over their targets were being deployed. Additionally, more anti-aircraft guns were being deployed around major targets, able to fire up to the height that airships used. To some extent, these threats could be avoided by reducing the weight of the airship, and flying higher. However, this brought with it its own set of challenges - oxygen starvation and cold, as well as light-weight structures that were unsuited for low-altitude flight. Meanwhile, the first large strategic bombers were coming into service. While each such aircraft could carry a smaller bombload than a single Zeppelin, they were easier to produce in large numbers, while being faster and capable of reaching similar altitudes. This meant that a bomber raid could do just as much damage as a Zeppelin raid, but was harder to catch. By 1939, twenty years of aircraft development had obsoleted the airship in most combat roles. Modern fighters could easily fly faster and higher than any airship, while bombers could avoid defences that airships couldn't. Bombers and transports were much more resilient than airships, which were much more expensive to replace when they were lost. Note that the US Navy, the prime user of airships post WWI and which used the inert helium as a lifting gas whenever possible, lost all but one of its rigid airships to accidents. Airships were also heavily limited by weather in a way aircraft were not. Rain or clouds could soak the skin, increasing weight dramatically, and reducing lift. They iced easily, again reducing lift. Hot weather meant that the usable lift was reduced. However, most importantly for the military, their abilities were greatly limited by wind. During the Zeppelin campaign against Britain in WWI, attacking airships frequently found themselves being blown off course - something that was much harder to do to a bomber. Airships only survived in the convoy escort role (a task they also excelled at in WW1) because this was a task that called for greater endurance than achievable with aircraft.