Mac Catalina - solution - CrossOver

[The Inept European]

Atlantic Fleet on Mac stopped working after the Catalina release that ended all support for 32 bit apps.

I have got Atlantic Fleet working on Mac Catalina using CrossOver by CodeWeavers. This is a paid for product though you can get a free trial. The process is to first install CrossOver, then create a 'bottle' that contains the Steam client. This is done through a simple UI, you just search for Steam, install it, run it, log in, download Atlantic Fleet into the 'bottle', run, and play.

No issues so far, I have done the Courageous scenario with no problem. (I even won the scenario, by the cunning expedient of sinking U-29 a split second before two torps were going to slam into the hull of Courageous.)