The Paris Gun would seem to qualify as an attempt to bomb civilians in WW1.
>...When the guns were first employed, Parisians believed they had been bombed by a high-altitude Zeppelin, as the sound of neither an airplane nor a gun could be heard. They were the largest pieces of artillery used during the war by barrel length, and qualify under the (later) formal definition of large-calibre artillery.
>...The German objective was to build a psychological weapon to attack the morale of the Parisians, not to destroy the city itself.
>...The projectile flew significantly higher than projectiles from previous guns. Writer and journalist Adam Hochschild put it this way: "It took about three minutes for each giant shell to cover the distance to the city, climbing to an altitude of 40 km (25 mi) at the top of its trajectory. This was by far the highest point ever reached by a man-made object, so high that gunners, in calculating where the shells would land, had to take into account the rotation of the Earth. For the first time in warfare, deadly projectiles rained down on civilians from the stratosphere"
https://www.iwm.org.uk/history/the-air-raids-that-shook-brit...