What is the scope used in submarines?

There are several primary official and unofficial uses for a submarine periscope:

Official

1. Surface search and recon while at Periscope Depth

2. Getting a satellite fix (embedded receiver)

3. Taking a Star or Sextant fix (if needed)

4. Target tracking and Ranging

5. Classified Intelligence gathering

6. Visual navigational fixes close to shore

7. Surface visual navigation in heavy weather (when bridge access isn't viable)

Unofficial

1. Periscope Liberty (looking at the ocean after you've been submerged for a few weeks)

2. Long-range scoping of babes on the pier while in port (most important function of all), especially during liberty port calls.

There are 2 periscopes aboard modern boats, the primary and attack scope. The primary is used for most functions, while the attack scope serves as the primary visual range and bearing scope for attacks (visual confirmation of a target is required, even if a submerged sonar track on the target is being performed), as well as serving as a backup. The attack scope has a much lower profile and is much harder to spot (leaves much smaller wake).