When was the periscope first used in a submarine?

Answer 1

The first rudimentary periscopes were used in experimental submarines in the mid-late 1880's - however, Simon Lake is generally credited with the invention of the telescoping periscope that is still in use today.

The new Seawolf, Virginia, and British Astute classes now use Photonics Masts rather than traditional periscopes. They're essentially HD optical sensors that relay information through a hull connection to workstations in the Control Room. This allows for a much smaller hull penetration than traditional scopes, and as such, it also allows for redesigns of the internal pressure hull, as the Control Room no longer needs to be directly under the Sail.

To be honest though, Photonics Masts limit the "cool" factor of periscopes. You just can't be like John Wayne looking at a video screen; you gotta have a traditional periscope.