When you travel on one of the brand new fleet of DFDS Seaways ferries, it takes about 2 hours to get from Dover to Dunkirk.
Dunkirk has direct links to the A16 and A25 motorways, so this route is more convenient than the Dover Calais route for travelling to many destinations in France and beyond.
Moreover, DFDS Seaways is the only ferry company sailing to Dunkirk.