How to use the Periscope...
T34
From gunners position
Left Shift + T to look down the sight then Left Shift + T again. Originally I thought that this was just a more zoomed in view.
When in this view use "Visor Horizontal Adjustment" My key settings which I think are default is Right Shift + , (comma) and Right Shift + / to swing left and right.
You will see in the top right of the screen the number of degrees you have moved the sight from the original point.
To re-set back to the centre (I assume where the barrel is pointing) "Reset Visor" Right Shift + ' (apostrophe)
M4A Sherman
From Commanders position (closed hatch)
Left Shift + V (Nestle to visor)
Right Shift + , (comma) and Right Shift + / to swing left and right
Right Shift + ; (semi colon) and Right Shift + . (full stop/period) to move up and down
To re-set back to centre - Right Shift + ' (apostrophe)
Panzer IV
From commanders position (closed hatch)
No periscope but Left Shift V gets close to the visor. Then repeating Left Shift + V moves clockwise around the turret to the other windows at right, right rear, left rear, left, front.