Convoy Attacks in 41 How do you do it??

[Breeze]

I am a noob to this game I have the bundle of the uboats and the wolves of the pacific I am playing the American Career and Im getting the hang of it but how do you guys sneak in on a convoy I had gotten a good ways ahead of a convoy I spotted threw down some markers of the travel paths of each ship and everything looked good dropped to 45 feet so i could use the periscope good when they got close had sub in silent running was waiting for first tanker to come up to me and as he was getting there the lead destroyer who seemed to go right by me was now behind me and blasting me. It seems these things always find me it is only 1941 and by the threads I read here that should still be easy any tips as to how you guys sneak in on a convoy?