I have several pictures of type XXI gun turrets and it looks like there is a box with a linkage attached ,so I would think that the aiming device is optical and most likely similar to the quad 20mm aiming device . As the 3 man crew was a gunner and 2 loaders this also makes me think it was aimed manually but moved in windage and elevation hydraulicaly . The radar on board this boat was not equiped as some think with the other hardware needed such as a computer or other device to calculate the lead on the attacking plane and other factors needed in a fully remote gun laying apperatus . The designers of this boat did not have AA guns planned but these were added later for the moral of the crew so they did not feel defenceless against an air attack . Since this boat was designed for underwater speed and was planned to stay mostly submerged and also the rushed into series production time frame a totally self contained , loaded ,aimed , tracking remote controlled gun turret was not high on the priority list . This was a feel good after thought and I would think that most , if not all boats were sunk or scuttled without those 20mm's even been test fired .