Slitherine

I am confused about the submarine rules in the mod. It seems like it makes them basically invulnerable. What's the rationale for this?

Also, is there any way to kill them?

The mod team was going for the most historically accurate representation of submarine warfare as a whole. In standard CEAW, the Allies can station DDs at key locations and attack subs that pop up halfway across the Atlantic. It was ahistorical that a ship nowhere near a sub when it learned of the sub's location could then go and attack it. And that system inevitably led to most if not all of the subs being destroyed by 1943 at the latest, in most cases.

In the GS/BJR mod system, DDs can only attack subs that pop up right next to them on the map, or withing a few miles in real life. This is historical. The system is also historical in that it allows German u-boats to menace Allied convoys and ships until the very end of the war.

Subs are not invincible, but they do require some effort to deal with. Strategic bombers are your best weapons, and good ASW research is a must. If you do these things, you will find that you can make subs pay for each attack later in the war. Early in the war the u-boats have the advantage, but that is historical too. And the convoys start out small and grow larger over time. Escort an important convoy with 2-3 upgraded DDs and you will find that subs seldom dare to attack it.

As you might be able to tell, the changes to submarine warfare remain my favorite aspect of GS. I fail to see how it could be done better within this game engine.

OK. Must get used to this. Very strange for me, who is used to the original game.