What an ON convoy designation meant

Where was an ON convoy bound?

ON identified an outbound North Atlantic trade convoy heading toward North America, in this case probably New York.

ON denoted outbound North Atlantic trade convoys bound for North America. The specific route in question was probably toward New York, although that destination is given tentatively. The designation supplies the route context for Brownrigg's final voyage with ON 16. It also helps decode similar convoy references elsewhere in Battle of the Atlantic records.