My best battle was SH5, not 4, but I'll post it here anyway
I get a contact report for a convoy, and plot an intercept course. I make contact with the convoy, and make a contact report. BdU orders me to keep contact without attacking, which I do. By early evening, U-339 arrives and attacks, sinking a freighter. While the escorts are busy with U-339, I move on the now unescorted convoy, and sink three freighters. With my tubes empty, I make my escape, with no offensive action at all taken against me.
BTW, good work using the crippled freighter as cover, I'll have to try that.