During the 18th and 19th century, the British Navy had ships all over the world, and communicating with them had to be difficult. After all, the Battle of New Orleans happened after the British had signed the Treaty of Ghent ending the War of 1812. Although many ship captains or fleet commodores had great freedom to operate tactically within their sphere of influence, what system of communication did the Royal Navy use to pass orders and receive reports from its ships far away? Assuming that orders had to travel by courier on fast sailing ships, did the Navy rely only upon its own ships to pass messages, or did it use fast commercial vessels? Was their a back-up system in case the courier was interecepted? Typically, how long did the process take?
Before the telegraph, communication was normally by post, which was an office or shack for handling the mail. Military communications were handled right alongside civilian messages and for this reason the post was almost always operated by the government. Each route went over land or by sea as was most convenient and sometimes both. In many cases private contractors would be employed to carry the mail between posts, in which case the packages of mail, called "packets" were sealed in some way to prevent the contractor from reading them. The business of carrying packets was called in England the "packet trade" and was a large business. Special, fast boats called "packet ships" were used to carry the packets and conduct other time-sensitive business.
Naval ships operated according to written orders and would periodically put in to a port to report and collect orders which would be found waiting for them. Military ships used the regular (Royal) post, except in very exceptional circumstances.
In places where maintaining a post was impossible due to cost or political considerations, then the Navy would try to use an embassy as the post. In very remote or dangerous places a standing ship would be used as the post.
Any British ship carrying official mail usually had a special pennant indicating that it was a mail ship.
They sent ships to the various headquarters with messages. Ships would return to their local headquarters to receive orders periodically. Failing that, the HQ would send another ship to the place where a particular ship was operating.
I suppose the navy might have used commercial ships if convenient, but in most cases had to use their own sloops and frigates for the purpose. Commercial ships usually lacked the crews for operating efficiently at high speeds and in foul weather.
As transoceanic trips could take weeks to months, this method took that kind of time.