To escort and guard Registered Mail pieces or other accountable items.
1. A number of merchant ships and/or naval auxiliaries usually escorted by warships and/or aircraft — or a single merchant ship or naval auxiliary under surface escort — assembled and organized for the purpose of passage together. 2. A group of vehicles organized for the purpose of control and orderly movement with or without escort protection that moves over the same route at the same time and under one commander.
convoy has been defined 2 different ways in documents like Glossary of Postal Terms, Department of Defense Dictionary of Military and Associated Terms.