In words which begin with the sequence <wr> the w is silent. Here are some words of this sort:
wrack wrangle wraith wrap wrath wreak wren wrestle wretch wretched wright wring wrist write written wrong wrote wrought
The addition of a prefix makes no difference, so, for example unwritten has a silent w.
The w is also silent in:
answer sword two
Of words beginning with <wh>, most of which have the pronunciation w, the following have a silent w and the sequence is pronounced h.
who whole whom whore whose