After the royal post office was driven off the mainland, it took refuge on one of the war vessels, which lay in New York harbour. The postmaster of New York received and opened the mails on board the ship, and all letters were advertised, so that they might be obtained either directly or through friends. The Americans, however, had a keen sense of the importance of communications, and from the beginning of the struggle, made every effort to intercept the packets. Early in May 1775, while the more cautious Americans were opposing any step that would lead to extremities, Finlay reported that he was on board the ship "King Fisher," and that a vessel manned by sixty resolute fellows was cruising about Sandy Hook, in the hope of intercepting the packet "Mercury," which was due to arrive.[103] In consequence of the burning of Falmouth by a British naval expedition, letters of marque and reprisal were issued in November by the province of Massachusetts Bay; and in the following March, the continental congress sanctioned the fitting out of private armed vessels to prey upon British commerce.[104] Seaport towns were enjoined that on no account should they furnish provisions to war vessels coming to them. The ministry were under no delusions as to the situation. At the end of September, the packets were withdrawn from general post office duty, armed as for war, and placed at the orders of the war office. The movements of the packets were clothed with secrecy, and it was only when the vessels were bound for Halifax that the public were notified that a mail was being despatched. From Halifax, the mails were taken by the first opportunity to Boston or New York. The attitude of the post office to all these preparations for war was very curious. It seemed incapable of understanding why exceptional measures were necessary at that time. A steady murmur of discontent was kept up against the war office. Remonstrance after remonstrance was directed against the commander-in-chief for the detention of the packets beyond what seemed a reasonable delay, and there was continual complaint against the restrictions placed upon the post office. Until the middle of the year 1776, although the service had been on a complete war footing for some months past, there had been no actual clash between the British and American vessels. The correspondence, however, reveals a state of great anxiety for the safety of the despatches, and as the vessels put out, the masters were placed under strict injunctions to sink the mails if there was any likelihood of capture.