The best example I can think of is GH Hardy's work on number theory. He was a pacifist and so specifically wanted to work on something that would not help the war effort. Fast forward 100 years and number theory now forms the basis of modern cryptography - securing everything from your banking details to military communications.
We often don't know what the applications are at the time, but that pure mathematics work very often forms the foundation of something important later on.
We often don't know what the applications are at the time, but that pure mathematics work very often forms the foundation of something important later on.