![Image](https://c1.staticflickr.com/5/4265/35520656621_82e8a610dc_o.jpg)
![Image](https://c1.staticflickr.com/5/4055/35528182311_b678e23ae5_o.jpg)
The PKB machine gun was a modified PK machine gun with removable spade grips and modified trigger. The the rotating TNPP-220 periscope directly in front of the bow gunner(s) is mechanically slaved to the machine gun port. This meant that wherever the machine gun was pointed, the periscope would accurately face the same direction. Elevation as well as horizontal traverse were both fully accounted for. The bow gunner would aim using a small scope on the right side of the TNPP-220 periscope, visible below.