Why did the English decide to establish a colony on Roanoke island?

The 1584 voyage was intended to establish a military basion in the New World. The plan was to find a hiding place where English ships could retreat after having raided the Spanish treasure fleet. The third voyage in 1587 was supposed to go to the Chesapeake Bay, not Roanoke Island. The colonists were landed at Roanoke Island - temporarily they thought - "But as soon as we were put with our pinnace from the ship, a gentleman--by the means of Fernandez--who was appointed to return to England, called to the sailors in the pinnace. He charged them not to bring any of the planters back again, but to leave them on the island"