If I remember correctly (and I&#x27;m still looking for a better source than this[1]), the Duke Of Wellington had requested a corps of longbowmen be made ready for use against the French in the Napoleonic wars, but was advised that no one with the skill needed to train them still existed (the training being the most difficult part of the technology). The last use of trained english longbowmen seemed to have been by some of the royalists during the English Civil War, and after the parliamentary victory practical knowledge of longbow archery as a military arm had been lost without anyone really noticing.<p>It&#x27;s hard for me to imagine a pivotal art or technology being lost like that, but I&#x27;m willing to bet its not at all uncommon if we look across history. For another military technology example, the art of dogfighting was deemed to have been lost for a brief period between WWII and the air war over Vietnam, and had to be re-engineered.<p>[1] <a href="http:&#x2F;&#x2F;everything.explained.today&#x2F;English_longbow&#x2F;" rel="nofollow">http:&#x2F;&#x2F;everything.explained.today&#x2F;English_longbow&#x2F;</a>