Using my 37mm flack gun when I had Stock Sh3 I could sink coastal and small merchants. GWX means its deck or nothing.
In Stock Sh3 I have sunk around 100,000 with the deck gun alone (there use to be a place where unescorted liners would come through like clock work in a two year time frame.
GWX I have sunk 36,000 with the deck gun, but as the years pass (i'm into 1943) the deck gun is getting less and less use.