Battle of Gravelines, 8 August 1588. The small port of Gravelines was part of Flanders in the Spanish Netherlands close to the border with France and was the closest Spanish territory to England. Medina Sidonia tried to regather his fleet there and was reluctant to sail further east, knowing the danger from the shoals off Flanders, from which his Dutch enemies had removed the sea marks. The English learned of the Armada's weaknesses during the skirmishes in the English Channel and concluded it was possible to close to within to penetrate the oak hulls of the Spanish ships. They had spent most of their gunpowder in the first engagements and had, after the Isle of Wight, been forced to conserve their heavy shot and powder for an anticipated attack near Gravelines. During all the engagements, the Spanish heavy guns could not easily be reloaded because of their close spacing and the quantities of supplies stowed between decks, as Drake had discovered on capturing the damaged "Nuestra Señora del Rosario" in the channel. Instead, the Spanish gunners fired once and then transferred to their main task, which was to board enemy ships as had been the practice in naval warfare at the time. Evidence from Armada wrecks in Ireland shows that much of the fleet's ammunition was unused. Its determination to fight by boarding, rather than employing cannon fire at a distance, proved a weakness for the Spanish. The manoeuvre had been effective in the battles of Lepanto and Ponta Delgada earlier in the decade, but the English were aware of it and sought to avoid it by keeping their distance.