One reason the escorts were generally not attacked was the poor chance of hitting them with a straight run torpedo. Given the hardware at his disposal, Doenitz was probably right in his order to concentrate on the merchants. On the other hand, the obvious way to win the Battle of the Atlantic was to sink the escorts, especially the escort carriers, in order to have an easier time of sinking the merchants. I do not know what Doenitz would have ordered had Lerche been available earlier, but you can see what he should have ordered. I suspect he may still have stressed attacking merchants since he was rather oblivious to losses. Doenitz spent too much time looking at the tonnage sunk graph and not enough time considering the tonnage sunk per U-boat and the losses per tonnage sunk data.

Zaunkoenig was supposed to be used on escorts, but it was rather inefficient for various reasons which have been discussed elsewhere and it too suffered from low priorities. Lerche was an improvement and certainly would have out foxed the Foxer.

The only way the wire guided torpedo was going to make a difference was when it was fired from an XXI. The key to winning the Battle of the Atlantic was the electroboat armed with wire guided torpedoes. The tactic would have been to let the best crews hunt the hunter killer groups and leave the convoy to the less experienced electroboat crews and the older snorkel boats.

Regards,
SuperKraut