From Dictionary.com:

Word Origin & History victuals c.1300, vitaylle (singular), from Anglo-Fr. and O.Fr. vitaille, from L.L. victualia "provisions," noun use of plural of victualis "of nourishment," from victus "livelihood, food, sustenance," from base of vivere "to live" (see vital). Spelling altered early 16c. to conform with Latin, but pronunciation remains "vittles."

Vitaille had no "c", and hence its English form was pronounced "vittle". Only later was the "c" added.