Bill,

There is a PDF document online about the modifications and different stages the U-505 went through during her service. I went ahead and looked it over, and it has a ton of very good information that applies to all the Type IX's including dates for specific modifications like the towers, guns, and deck styles. Here is a link to it-

[amp.rokket.biz]

It helped me on a few questions I had about my U-550 project. If anything new comes up for the early war towers, I will definatly pass it on.

Cheers!

Jon