How submarines determine where they are and how they measure how far away something is?

All submarines have several methods by which they can determine a general navigational position or a precise navigational fix:

1. GPS Satellite Network or SatNav fix

2. Electronic Gyroscope

3. Dead Reckoning plot

4. Radio Bearing

5. Visual Aid (close to shore, e.g., lighthouse, landmark, etc.)

6. Sunline (Sextant can be used when surfaced, or attached to Periscope while submerged)

7. Radar

For target range calculation, it depends on whether or not it's a visual and Sonar target, just visual, or just on Sonar. Visually, range markers on the Periscope indicate estimated range, however unless circumstances warrant, that range will always be verified and compared with Sonar range.

Sonar ranges are determined over time by tracking the target through induced turns (zigs), either by the submarine or the target. Either way, the change in direction adds another leg to the target tracking solution; eventually an estimated range based on known, sound trigonometric calculations weil be formulated, either by computer (normal) or by hand (backup). The tracking solution takes into account several known variables given by Sonar:

1. Estimated target speed (RPM) and type (e.g., Merchant, Warship, Trawler, etc.)

2. Sonar bearing

3. Closing or Opening Range (target getting closer or moving away)

Sonar's given target tracking information is based on the current sound profile for the given operating area the submarine is in, as all information is based on the current speed of sound in water, which can change.

In the end, target speed, bearing, and course are the key factors in determining range prior to a torpedo shot; however, in most circumstances, the shooting submarine will check a target's range with all other information plotted with active Sonar echo ranging (usually only 1 or 2 pings to verify range). If the range matches the plot, the information is fed into the torpedo guidance computer prior to shooting.