Spanish if needed, although he was forbidden from engaging them in battle until joined by the rest of the fleet, some fifty vessels under Johan Evertsen. Tromp divided his force into three; 12 ships under Joost Banckert were positioned north of the Downs, in the unlikely event the Spanish took the long route around the British Isles. Five ships under Witte de With patrolled the English side of the Channel, while the remaining 12 under Tromp monitored the French coast. Preliminary actions; 16 to 18 September Attempts by the French admiral Henri de Sourdis to disrupt Spanish preparations failed and the fleet sailed on 27 August, entering the Channel on 11 September. Ships of different squadrons were mixed through the formation, an attempt to ensure smaller ships would be supported by larger ones. The vanguard was composed of thirteen ships from the Armada de Flandre under Miguel de Horna, since they had the most experience in these waters; De Horna himself accompanied Oquendo on board his flagship. On 15 September, they learned from a passing English ship that a Dutch squadron was anchored near Calais and the next day made contact with Tromp. Following his instructions, Oquendo adopted a half-moon formation, placing his flagship on the right flank; despite being outnumbered, Tromp placed his squadron into line of battle and attacked. Oquendo used the same tactics employed in his 1631 victory at Abrolhos, where he had destroyed the Dutch flagship in a single ship to ship battle. He failed to issue adequate instructions to his subordinates and negated his superior numbers by constantly seeking to engage Tromp's flagship. This manoeuver, however, was effected without warning the rest of the Spanish fleet. Some of the ships near Oquendo turned with him, others were confused and maintained bearing. The half-moon formation quickly disintegrated, and only the Dunkirk squadron and the galleon San Juan kept up with the Spanish flagship's pursuit of Tromp. Had Oquendo given the order for a line, the immense Spanish fleet could have probably encircled and dispatched the Dutch squadron in a few hours. However, Oquendo seemed intent on boarding the Dutch flagship. When he finally decided to turn for a shot, he did it too late and sailed past the Tromp's poop. Trying to correct his error, Oquendo attempted to board the second ship in the Dutch column. The latter also avoided him. Oquendo's flagship and one of