The two fireships were successfully used in the night of 4–5 April 1585. Giambelli had prepared 32 normal fireships to be first launched in several waves to deceive the Spaniards. In fact the commander supervising the operation, Vice-Admiral Jacob Jacobsen, set all ships on their course in quick succession, from fort "Boerenschans", the hellburners last. The current and ebb tide carried the ships towards the bridge. The decks of the hellburners were piled with wood and small charges with slow fuses, which gave the impression that they were conventional fireships, causing the Spanish troops to try to extinguish the fire.