At this point the Commissioner immediately sought assistance from the Admiralty, sending a pessimistic message to the Navy Board, lamenting the absence of Navy senior officials whose help and advice he believed he needed. The thirty ships were those of Van Ghent's squadron of frigates. The Dutch fleet carried about a thousand marines and landing parties were dispatched to Canvey Island in Essex and opposite on the Kent side at Sheerness. These men had strict orders by Cornelis de Witt not to plunder, as the Dutch wanted to shame the English whose troops had sacked Terschelling during Holmes's Bonfire in August 1666. Nevertheless, the crew of Captain Jan van Brakel could not control themselves. They were driven off by English militia, and found themselves under threat of severe punishment upon returning to the Dutch fleet. Van Brakel offered to lead the attack the next day to avoid the penalty. Charles ordered the Earl of Oxford on 8 June to mobilise the militia of all counties around London; also all available barges should be used to lay a ship's bridge across the Lower Thames, so that the English cavalry could quickly switch positions from one bank to the other. Sir Edward Spragge, the Vice-Admiral, learned on 9 June that a Dutch raiding party had come ashore on the Isle of Grain (a peninsula where the river Medway in Kent, meets the River Thames). Musketeers from the Sheerness garrison opposite were sent to investigate. Only in the afternoon of 10 June did Charles instruct Admiral George Monck, Duke of Albemarle to go to Chatham to take charge of matters, a full three days later ordering Admiral Prince Rupert to organise the defences at Woolwich. Albemarle went first to Gravesend where he noted to his dismay that there and at Tilbury only a few guns were present, too few to halt a possible Dutch advance upon the Thames. To prevent such a disaster, he ordered all available artillery from the capital to be positioned at Gravesend. On 11 June (Old Style) he went to Chatham, expecting the place to be well prepared for an attack. Two members of the Navy Board, Sir John Mennes and Lord Henry Brouncker, had already travelled there on the same day. When Albemarle arrived, however, he found only twelve of the eight hundred dockyard men expected and these in a state of panic; of the thirty sloops only ten were present, the other twenty having been used to evacuate the personal possessions of several officials, such as Pett's ship models.