The Armada anchors off Calais on July…

The Armada anchors off Calais on July 27 in a tightly packed defensive crescent formation, not far from Dunkirk, where Parma's army, reduced by disease to sixteen thousand, is expected to be waiting, ready to join the fleet in barges sent from ports along the Flemish coast.

Communications have proven to be far more difficult than anticipated, and it only now becomes clear that this army has yet to be equipped with sufficient transport or assembled in port, a process which will take at least six days, while Medina Sidonia waits at anchor; and that Dunkirk is blockaded by a Dutch fleet of thirty flyboats under Lieutenant-Admiral Justin of Nassau.

Parma desires that the Armada send its light petaches to drive away the Dutch, but Medina Sidonia cannot do this because he fears that he might need these ships for his own protection.

There is no deepwater port where the fleet might shelter—always acknowledged as a major difficulty for the expedition—and the Spanish find themselves vulnerable as night falls.

At midnight on July 28, the English set alight eight fireships, sacrificing regular warships by filling them with pitch, brimstone, some gunpowder and tar, and cast them downwind among the closely anchored vessels of the Armada.

The Spanish fear that these uncommonly large fireships are "hellburners", specialized fireships filled with large gunpowder charges, which had been used to deadly effect at the Siege of Antwerp.

Two are intercepted and towed away, but the remainder bear down on the fleet.

Medina Sidonia's flagship and the principal warships hold their positions, but the rest of the fleet cut their anchor cables and scatter in confusion.

No Spanish ships are burnt, but the crescent formation has been broken, and the fleet now finds itself too far to leeward of Calais in the rising southwesterly wind to recover its position.

The English close in for battle.