 Ever since its actions in Denmark in 1659, involving many landings to liberate the Danish Isles, the Dutch navy had made a special study of amphibious operations; the Dutch Marine Corps was established in 1665.After the Four Days' Battle, a Dutch marine contingent had been ready to land in Kent or Essex following a possible Dutch victory at sea.The Dutch fleet was, however, unable to force a safe passage into the Thames as navigational buoys had been removed and a strong English squadron was ready to dispute their passage.