Port Royale 3

This requires a convoy to be listed as ‘active’ on a single trade route for 365 game days. Provided the convoy is not attacked or deactivated you can check how long it’s been active by pressing RB and scrolling across to the convoy tab. This will probably come naturally as you progress through the game, but to increase the chances of the convoy not being attacked, be sure to have a number of warships (with maximum sailors and weapons) included in the convoy.