When Nautilus made her historic transit from the Pacific to the Atlantic via the polar route in the early 1950s she did so submerged and on nuclear power. The world wide acclaim due this first nuclear submarine was predicated on the amazing feat of winding her way through the uncharted and menacing ice that hung like inverted mountains from the surface of the frozen ocean. To accomplish this the submarine had been equipped with forward, side scanning and up-down sensing sonar transducers. The boat "saw" her way through the ice fields by constant pinging.

Such use of active sonar while transiting oceans today would violate a submarine mission's protocol to remain undetected. A modern boat uses active sonar for soundings in a judicial manner. Thus, a modern submarine relies upon the accuracy of its navigation and the reliability of the bottom information at hand to keep it from harm's way.

The modern submarine has at its disposal a variety of navigational information not known to the crew of the Nautilus. Of course, it still has the traditional methods of dead reckoning and celestial observation to back up its sophisticated electronic information. During the 1950s a navigator relied upon Loran which was based upon electronic signals emitted from fixed positions around the globe linked to slave stations. The submarine fixed its position by intersecting hyperbolas. It worked fine for its day, but was primitive by today's standards.

Much of a modern submarine's ability to navigate accurately is a product of the Navy's early interest in building a submerged launching platform for missiles. In order for the missile to hit a target it was necessary to know the exact position of the submarine launching it. Early attempts at accurate electronic navigation included RAFOS, a gravimetric system which relied upon gravity deviations and SOFAR which dangled a small explosive device over a sea's bottom, recorded the explosion's echo and compared that to known information about bottom topography. Neither OF these methods proved to be very reliable.

In the 1960s the development of the SSK program necessitated the use of more sophisticated navigational methodology. These sonar picket boats had to remain in a geographical area and to do this they had to know exactly where they were. Navigation became critical and the Navy stepped up its research in this area.

TROUNCE was the first step toward an inertial navigation system. It required an emission from a radar equipped periscope to track a guided missile. With the development of the stabilized periscope for azimuth sights, accurate navigational inputs to an inertial system of tracking became possible. SINS may be thought of as a computerized dead reckoning using extremely accurate inputs including an electromagnetic log, star-tracker periscope with radiometric sextant and NAVDAC for ground speed measurement. It verifies its information through ground comparisons.

The SINS system is now an augmentation for satellite navigation which uses fixed satellites and on-board receptors/computers. Indeed, the electronics technician-nav specialist (the old quartermaster rate) often uses a commercial hand-held computer that reads longitude and latitude accurate to the fraction of a minute.

The probability that a submerged submarine knows exactly where it is at all times is extremely high. It need not rely upon any single system, but uses all its inputs from sophisticated electronic and computerized information to simple dead reckoning using a log and compass heading.

It is not enough to know where a submarine is to insure safety of submerged transit. It is essential to know how much water is under the boat's keel. How does a submarine make this determination? The simplest method is to take a sounding, but as stated above this is done sparingly and only then to verify what is shown on charts.

Chart information comes from several sources including the Coast and Geodetic Survey, the United States Hydrographic Office or the Naval Oceanographic Office and its international equivalent. At the outset it should be noted that the modern submarine has bottom information from computerized electronic displays as well as paper charts known to all submariners. Computerized electronic displays are only as accurate as the information stored in its computer. These displays are most often applicable to harbors, coasts, channels and other thoroughly explored areas. As the transiting submarine moves into open water under the high seas it shifts its navigation emphasis to paper charts. The navigator uses both devices to keep track of where the submarine is in relation to the depth under the keel.

The reliability of charts and electronic/computerized displays is a function of the organizations that produce the information and the adequacy of the information availability. A cursory inspection of the organizations include:

1. The Coast and Geodetic Survey
   This organization is charged with triangulation and measurement of the sea's bottom irregularities and elevations using base line measurement; geodetic astronomy including longitude, latitude, azimuth and time; advanced computational methods; gravitational studies and magnetism. The resulting information is distributed to other organizations which translate the information into useful representations for mariners. The organization focuses its attention on the detail of coastal areas.
2. The United States Oceanographic Office
   This organization is charged with the responsibility of producing the charts, navigational aids and books used by navigators of the United States Navy. Under the supervision of the Secretary of the Navy, the Office exchanges information with equivalent offices in foreign nations. Outlets for the Office may be found in Jacksonville, Florida, Norfolk, Virginia, Pearl Harbor, Hawaii, Rota, Spain, San Diego, California and Yokosuka, Japan. One of the key functions of the Office is the Naval Oceanographic Office Major Shared Resource Center. This center provides high performance computing services and support to the United States Navy. It develops and distributes vector and scalable software for use in navigational computers. It collects and stores data on environmental changes such as iceberg movement and seismic activity which effects the accuracy of chart sea depth information.
3. The International Hydrographic Organization
   The United States Oceanographic Office, formerly known as the United States Hydrographic Office is a participant in the International Hydrographic Organization. The purpose of this organization is to ensure the provision of adequate and timely hydrographic information for world-wide marine navigation through the endeavors of the participating national hydrographic offices. Its main focus is the production of nautical charts using cartography which describes the features of the seas and coastal areas in terms of water depth, nature of bottom, elevations, configuration and characteristics of dangers to navigation. Its products include geographic information in digital format for computer software. The world charts are divided into sixteen areas exclusive of the polar regions.

A United States submarine carries as many of current charts as may be needed for the intended transit and operation. Charts may be overlapping in that area charts may be supplemented by larger scale charts showing more detail of a specific underwater terrain. Additionally, a submarine navigator insures that it has the latest information in digital form for use in its electronic/computerized displays.

There is little question that a modern submarine knows exactly where it is at all times. The only limitation on depth-below-the-keel information lies in the reliability of the information in the on-board charts produced by the above organizations.