 Grand Port was an easily defensible natural harbour because the bay was protected from the open sea by a large coral reef through which a complicated channel meandered, known only to experienced local pilots.Île de la Passe was vitally important in the control of Grand Port because it featured a heavy battery that covered the entrance to the channel, thus controlling the passage to the sheltered inner lagoon.The British planned to use the troops on "Nereide", under her captain Nesbit Willoughby, to storm Île de la Passe and capture the battery.