A relief effort was organised by a fleet of English and Dutch troops under Sir Robert Dudley, Earl of Leicester, Governor-General of the United Provinces.

[2][6][7] Leicester landed a force of 4000 foot, 400 horse at Ostend, to cut Parma’s communications, but called his men back to the fleet before coming to grips with any Spaniards; while a sea-borne attempt to force the channel and relieve the town was similarly aborted: Garrett Mattingly concluded that “The chief effect of this fortnight of imbecile manoeuvres was on the morale of the beleaguered garrison”.

[9] The loss of the English-held port of Sluis revealed the inability of Leicester to assert his authority over the Dutch allies, who failed to cooperate successfully in relieving the town,[10] and led to recriminations between the governor-general and the States of Holland.

[13] On 16 December 1587, Leicester returned to England,[13] where the privy council tried in vain to hold him to account for his failures, protected as he was by the favour of the Queen.

[14] By contrast, Parma had gained a strategic prize that enabled him to move barges by inland waterways from the Scheldt to Dunkirk, preparatory to the coming of the Spanish Armada.