By the time the Battle of Königgrätz rolled around, the Dreyse needle gun had been around for years. However, it seems to have been one of the major contributors to the Prussian victory in that battle, and in the war overall.
Did the French not know about the gun’s capabilities for some reason, or did they know about it, but fail to accommodate for it in their strategy and tactics?
More generally, how well did European nations understand one another’s materiel capabilities, and strategic and tactical doctrine in the mid 1800s?
The French had actually noticed the advantages of the Dreyse needle-gun in the Prussians' earlier wars against Dennmark and Austria. When it was their turn to get sucked into one of Bismark's "combinations", the French had something actually better: the 1866 Chassepot. The Chassepot was a bolt-action, like the Dreyse, and like the Dreyse did not use a metallic cartridge. But it had some improvements : The percussion primer was at the base of the cartridge, and so there could be a larger powder charge. As a result the Chassepot had a longer range than the Dreyse.
During the Battle of Sedan, the few French units that had dug themselves trenches were sometimes able to take advantage of their longer effective range of fire and stymie German infantry assaults. But the French were also generally out-maneuvered. Their commanders ( especially their king, who wanted to be a commander) did not judge the terrain and opposing forces well, and those units who were entrenched were also not able to resist German artillery fire. After the surrender the Germans took home a large number of Chassepots, and later would convert them to 11mm Mauser and give them to some of their own troops.
The French losses after the Franco-Prussian War caused French resentment, of course, and resulted in a very intense arms race until WWI. The German Dreyse was met with the 1866 French Chassepot, the Germans then responded with the 1871 Mauser, the French updated their Chassepot to the 1874 Mas, the Germans updated their 1871 Mauser to become a magazine rifle in 1874, under the prodding of the revanchist General Boulanger the French developed smokeless poudre B in 1882 and the Lebel rifle soon after, the Germans introduced their own smokeless-powder rifle in 1888, then the more high-powered Mauser 98 with a box magazine, the French responded with their own 1909 Berthier. And , of course, there was also a race to improve artillery, buy machine guns,....until in 1914, it all got used.
Addendum: I realize that this may sound like I’m chalking up the Prussians’ victories to their superior military technology, rather than their overall strategy over the course of the war. However, histories of the F-P war seem to stress the importance of the Dreyse needle gun quite a bit, and I wanted to focus on that component.
