The conflation of SIGINT and cryptology makes me doubt the writer's understanding of the field. While cryptography and cryptanalysis have long been important to the field, they are but one aspect. I won't offer a meaningless percentage as to how important they are, but consider the importance of a) traffic analysis and b) meta-data: There are plenty of historical examples of operational decisions being made on the basis of traffic analysis and there is the oft-quoted Michael Hayden's "we kill people based on metadata".

(Then there is my favourite WWII nit: The focus on Enigma, which, while undoubtedly important, pales in comparison to Tunny. The fact that Flowers could build essentially a general purpose computer to crack a cipher based only on its apparent properties is heads-and-shoulders and all other superlatives above Enigma, for which GCHQ had working examples throughout the war. I am not downplaying the importance of the Enigma cryptanalysis work, merely suggesting that Tunny was, in the end, and strategically, far more valuable, especially once telephone communications became harder for OKW.)