In the more than two hundred years after the development of the musket, body armor had been obsolete. Ten generations of soldiers had marched into battle wearing only wool or cotton uniforms and caps, often in fanciful colors that would stand out through the haze of black powder smoke. But in 1915, military physicians on all sides urged a return to the use of armored helmets to protect against head wounds. The medieval had become modern.
The British Army looked back to the medieval “kettle hat” for inspiration. Originally designed to shield feudal infantry from overhead blows by mounted knights and castle defenders, it became the basis for the iconic “Brodie Helmet” used by British, Commonwealth, and American forces. Some Brodie helmets remain in use to this day, particularly in post-colonial militaries that received British supplies.
The Germans drew their inspiration from the late medieval sallet, which resulted in the “coal scuttle” shaped Stahlhelm used by German military forces in both World Wars. The Stahlhelm fell out of use in Germany after it became associated with militarism, but it was distributed to countries around the world and continues to be worn by the Chilean military for ceremonial purposes (I’ve seen them!).
The French, interestingly, did not look back to the Middle Ages for guidance but instead modeled their Adrian helmet on the traditional helmets of Parisian firefighters. The Adrian helmet was distributed widely to Allied armies during the war and was quite popular due to its stylish lines compared to the alternatives. Unfortunately, the Adrian helmet was also less resistant to bullets than the other two models and was often one of the first items to be discarded during a retreat. Nonetheless, the Adrian helmet saw use by French, Soviet and other forces through World War II.
The way that history can fold back on itself, making ancient technologies and strategies suddenly relevant again, can serve as inspiration for speculative fiction writers. A common trope in space opera, for example, is to imagine space combat functioning more like Napoleonic sea battles, submarine warfare or some other historical model. So long as the imagined rules and technologies are internally consistent in supporting this depiction, it’s a valid and useful option for writers to look to history for ideas that can be translated into their universes.
Fantasy, too, can benefit from this insight by making the new old again. Consider how modern social and technological changes could be reflected backwards into a typical medieval-type fantasy due to the presence of magic or other changes. The 18th and 19th Centuries are particularly valuable sources of inspiration, as they have one foot in modernity and another in the world of horse-drawn, agricultural societies dominated by aristocrats.
Update: And speaking of the medieval becoming modern…