What role did the Persian navy play in military conquest?

We don't associate a land-based power like Persia with sea conquest. Yet, Persia had a very strong navy that was constructed by and manned by subject peoples including Ionian Greeks, Egyptians and Cypriots, all of whom had a history of successful shipping industries. Cambyses' conquest of Egypt and the Greek Wars fought by Darius I and Xerxes would have been impossible without a navy. This source-based homework task is designed for students of the NSW Ancient History Syllabus for the Australian Curriculum.

Higher School Certificate course
Historical Periods
Option D: Persia - Cyrus II to the death of Darius III

Historical Societies
Option D: Persia in the time of Darius II and Xerxes