Though I think WWI is an even better example. The machine gun wasn't even that new at the time and had been used in the british colonies, but no European power had themselves faced them and turns out they not only didn't have any idea how to approach them, but apparently didn't even spend much time thinking about it because they started the war with fucking calvary charges. And I mean calvary as in aristocrats in expensive armor riding horses, riding out into what would later be known as "no man's land" to get mowed down by machine guns.

Followed by three years of pretty much just trying that only without the horses and more men until Germany ran out of bullets and had to surrender.