The Post Office Packet Service dates to Tudor times and ran until 1823, when the Admiralty assumed control of the service. Originally, the Post Office used packet ships to carry mail packets to and from British embassies, colonies and outposts. The vessels generally also carried bullion, private goods and passengers. The ships were usually lightly armed and relied on speed for their security. However, Britain was at war almost continuously during the 18th and early 19th centuries with the result that packet ships did get involved in naval engagements with enemy warships and privateers, and were occasionally captured.

Generally, packet trade is any regularly scheduled cargo, passenger and mail trade conducted by boat or ship. The boats or ships are called "packet boats or packet ships" as their original function was to carry mail.