Complex sentence: The local militia commander had been warned that trouble was afoot, and when a Hunter vessel attempted to land in the middle of the night at a wharf on the Prescott waterfront, it was fired upon by alert Canadian militiamen.
Split into simpler sentences: The local militia commander had been warned that trouble was afoot. When a Hunter vessel attempted to land in the middle of the night at a wharf in Prescott, it was challenged and fired upon by alert Canadian militiamen.