What function does a periscope do on a submarine?

Answer 1

Periscopes have several primary functions:

1. Visual verification & identification of current Sonar targets.

2. Navigational fixes by using visual references (near shore or by use of attached sextant for star fixes).

3. Aiding in target tracking/range calculation.

4. Bearing, Speed, Angle on the Bow and Range match with Sonar and Fire Control prior to weapon shot.

5. Visual detection of any targets not picked up by Sonar due to poor sound conditions.

Due to the way sound propagates in the ocean, it is possible to perform a Sonar sweep and not have any close-aboard (collision range) targets on sonar. However, when coming to Periscope Depth, if there is a thermal layer blocking sonar and any targets, it is essential to get a quick ID, range and bearing to any close-aboard target that may have been undetected by sonar. This is why the periscope is so important when ascending to PD. The Con officer can then order the helmsman to steer clear or emergency dive to avoid any close-aboard contacts.

Visual verification, bearing and range are matched against Sonar's target information for 3 reasons:

1. You don't want to shoot anything you're not supposed to.

2. Sound propagation and ocean properties can alter the actual received target bearing, and hence the estimated range.

3. Visual verification, bearing and range via periscope ensures the best target solution for the torpedo before shooting.

Of course this only applies to surface targets, and not submerged submarines. In such cases, a sonar-only target solution is used and fed into the torpedo guidance system prior to shooting.