Just last week when I reported 2 merchants and a destroyer, a nice squadron of Flugzeuge came about 19 minutes after I reported it. They sunk one merchant and damaged the destroyer leaving it without depth charges.
It's pretty much random. However when I spot a ship, identify it and report it, I do get support. But you need to wait quite a bit, and when the support does show up, if they ever do show up, it's usually planes. I still need to see a ship at my rescue.
