Ironically, they even wrote essays glorifying pure mathematic's uselessness:

> > No one has yet discovered any warlike purpose to be served by the theory of numbers or relativity, and it seems unlikely that anyone will do so for many years. [1]

> Since then number theory was used to crack German enigma codes and much later, figure prominently in public-key cryptography. https://en.m.wikipedia.org/wiki/A_Mathematician's_Apology

[1] Hardy's "A Mathematician's Apology" http://www.math.ualberta.ca/~mss/misc/A%20Mathematician's%20... [pdf]