In the control room (where the navigator stands in front of his map) you will see the observation scope...click on it...
then walk up the ladder leading to the bridge. inside the conning tower you will see the attack scope...walk towards it and click on it....
And don't ask me where the control room is
(If you are using TD's New UI you can also teleport to these scopes / different stations by the click of a button)...Press F1 for keyboard layout and to see which buttons raise/lower your scopes)