Earlier quoted context omitted.
There's no letter-to-sound correspondence in English. English probably - at least compared with other European language - is one of the most irregular languages in terms of pronunciation: http://www.wordsmith.org/awad/english1.html This is simply due to the language having been heavily influenced by a host of other - quite different - languages over the centuries, Old Norse and French in particular. There's also the…
English was not "influenced" by Old Norse, rather, they are siblings
However, in the Early Middle Ages English was also heavily and directly influenced by Old Norse because Vikings at that time not only more or less continually invaded the English east coast but also settled and established their own jurisdiction (The Danelaw) there.