Dunkirkers During the Dutch Revolt ( 1568 – 1648 ) the Dunkirkers or Dunkirk Privateers , were commerce raiders in the service of the Spanish Monarchy . They were also part of the " Dunkirk fleet " , which consequently was a part of the Spanish Monarchy ' s " Flemish fleet " " ( Armada de Flandes ) " . The Dunkirkers operated from the ports of the Flemish coast : Nieuwpoort , Ostend , and in particular Dunkirk . Throughout the Eighty Years ' War , the fleet of the Dutch Republic repeatedly tried to destroy the Dunkirkers . The first Dunkirkers sailed a group of warship s outfitted by the Spanish government , but non - government investment in privateering soon led to a more numerous fleet of privately owned and outfitted warships . Origins and function . Dunkirk was in the hands of the Dutch rebels from 1577 until 1583 , when Alexander Farnese , Duke of Parma re - established the sovereign ty of his uncle Philip II of Spain as count of Flanders . Dunkirk was , at the time , an important , strategically positioned port with its approaches shielded by sandbanks . In 1583 , Parma assembled a small royal squadron of warships to destroy Dutch naval trade and fisheries . However , it did not take long before the Habsburg authorities in the Low Countries began issuing letters of Marque , and privately owned warships filled the ranks of the Dunkirkers . These privately owned warships were known in Dutch as the " particulieren " , to distinguish them from the royal warships that were also part of the fleet . At their peak , the Dunkirkers operated about a hundred warships . The crews were mostly made up of Flemish fishermen , supplemented with Walloons , Spaniards and many individuals from the Northern Netherlands and other European countries . Apart from targeting trade and fishing , the royal squadron was often used to convoy troops between Spain and the Spanish Netherlands . Effectiveness . Despite a near constant blockade of the Dunkirkers ' ports by Dutch warships , the privateers routinely managed to evade the blockaders and inflict damage on Dutch shipping . Though the Dutch at times prevented the Dunkirkers from reaching open sea , during the winter months the blockade was extremely difficult to maintain and permitted virtually free passage . Sometimes naval battles ensued when privateers tried to break out or when Dutch warships tried to destroy the privateers in their harbours . During one of these Dutch attacks , the Dutch folk hero Piet Pieterszoon Hein , famous for capturing a Spanish treasure fleet , was killed . The Dutch declared the Dunkirk privateers pirates in 1587 ; captains of Dutch naval vessels had to swear an oath that they would throw or beat all prisoners from Dunkirk warships into the sea ( euphemistically known as " voetenspoelen " , " washing the feet " ) . Due to its excessive harshness and the fact that it provoked equally cruel retributions from the side of the privateers , this standing order was very unpopular with Dutch crews and the general public . The order was often evaded by putting Dunkirk seamen off on one of the many shallow shoals off the Flemish coast from which they could wade to dry land . The Dunkirkers had an extremely wide range for their era . Although mainly operating in and around the Channel , they also sailed near the Danish and German coastal areas to intercept Dutch ships returning from the Baltic , and operated in Spanish and Mediterranean waters . They cooperated closely with the Spanish navy , for instance , in the Battle of the Downs . This combined effort reached a peak of effectiveness during the time the Eighty Years ' War merged with the Thirty Years ' War . To evade the Dutch navy the Dunkirk admiralty had a special type of small and very maneuverable warship constructed , the frigate . Frigate - like ship types were soon adopted by many professional navies and still have their modern - day counterparts . In 1600 the Dutch sent an army to conquer the city of Dunkirk and stop the privateering once and for all . The Dutch invasion force clashed with a Spanish army and although the Dutch won the resulting Battle of Nieuwpoort the Dutch commander , stadtholder Maurits of Nassau , realised his lines were dangerously over - stretched and so turned back to the Republic . The Flemish Fleet continued to be especially damaging to the herring fisheries of Holland and Zeeland , almost completely wiping out the sector on several occasions . However , Dutch merchantmen proved far more valuable targets , sometimes vessels on their way back from Russia or as far as the Indies were captured , along with their valuable cargoes . After 1621 , when the Twelve Years ' Truce ended , the Dunkirkers captured on average 229 merchantmen and fishing vessels per year from the Dutch . During this period they took about sixty English vessels each year , as neutral shipping carrying munitions and victuals to the enemy were also considered ' good prize ' . This was one of the major concerns of Charles I of England ' s diplomatic representative in Brussels , Sir Balthasar Gerbier , who eventually managed to have tobacco taken off the list of ' victuals ' . One of the most successful raiders of this period was Jacob Collaert . It was not until October 1646 , when the French captured Dunkirk with Dutch naval support , that the danger from the privateers was greatly reduced . In 1652 , Spanish forces recaptured the city and the Dunkirkers once again became a major threat . The Dunkirkers wiped out English trade after England resumed hostilities against Spain in 1654 , before Dunkirk was captured by a Franco - English force in 1658 . Ostend then became their most important port . When , after 1672 , France and the Dutch Republic became enemies , privateering activities were resumed at Dunkirk , this time for France , and this would last intermittently until 1712 . A famous Dunkirk privateer from this period was Jean Bart .