The Pequot's Navigation and Magnetic Deviation Systems  

These pages tell the story of the U.S. Coast Guard Cable ship Pequot during World War II as a harbor defense cable-laying and repair ship under direction of the US Navy. This site presents details of the ship's navigation and magnetic deviation systems in use during the laying anti-submarine indicator loop cables. During the 35 years that the USCG Pequot was at sea, navigation was accomplished through the use of nautical charts and compass readings.

Nautical Chart: When steaming along the rocky coast of Maine during WWII the Pequot’s navigator and captain would use the ship’s compass and a nautical chart such as this one from 1944. A close-up on the right shows numbers in the ocean which indicates the depth of water in fathoms, with one fathom equal to 6 feet. (US Coast and Geodetic Survey 1944)
Click image to enlarge. 
A section of the Nautical Chart Abbreviations used with the charts opposite. (US Coast and Geodetic Survey January  1941)
Click image to see a full sized view.

Binnacle: During the 1940s directly in front of the helm in the pilothouse was a John E. Hand & Sons 8" liquid Compensating Pedestal Type Spherical Compass Binnacle. This was the ship's primary navigation compass when she first went to sea.

118. We can see the placement of the steering binnacle in the pilot house on the 1908 construction plans.

119. A typical Compass binnacle of the period with red and green iron spheres (quadrantal spheres) used for magnetic deviation adjustments. (Antiques of the Sea, Lionel Corporation Binnacle 1944)

The "binnacle" is a watertight stand which holds the ship's magnetic compass. It is designed to be seen by a helmsman standing at the ship's wheel. Consisting of a circular base, a pedestal, a magnet compartment, and a chamber where the compass 'floats' in a metal ring in a bowl of alcohol on two pivots, the binnacle's gimbals keeps the compass level despite the motion of the ship. Early binnacles had a small oil lamp mounted on one side of the compass for night viewing. Electric lighting systems were introduced later.

Mounted 21' above the Pequot's main deck and 60' from the stern the "After Deck House" Compass on Pequot was an E. S. Ritchie and Sons 8"  liquid Type 7, (#49 U.S. Navy Bureau of Navigation Machinery Division) Compass Binnacle that had been on the ship since January of 1919.  This "back-up" compass was located on top of the rear deck cabins so it would be as far away from the magnetic signature of the steel hull as practical.

120. The After Deck House compass binnacle is clearly detailed in the 1908 elevation construction drawings.

121. Just aft of a life raft on top of the officer's staterooms we can see the exterior compass binnacle with its distinctive iron adjustment spheres. (Calamaio Family)

These critical navigation compass binnacles were periodically re-calibrated to compensate for the difference or "deviation" of true north from magnetic north, and adjusted for the magnetic influence of the ship's steel hull.  Changes in the magnetic signature of the hull after deperming and degaussing during WWII only complicated matters. 

Captain Matthew Flinders of the  Royal Navy, determined that erecting a vertical metal bar in front of the compass allowed adjustments to be made for magnetic deviation.  Those bars were named Flinders Bars in his honor.  Later, Sir George Airy, the Astronomer Royal, discovered that the accuracy of the magnetic compass could be further improved by placing quadrantal spheres (large balls of soft iron) on either side of the compass.  Both the Flinders Bar and the quadrantal spheres, along with various adjustable compensating magnets, for correcting the compass were part of the Pequot's compass binnacles.

122. An April 10th 1942 Deviation Table shows adjustments were made to correct for 17 Degrees of deviation. At that time Lars Sande was the ship's Navigation Officer. The commanding officer was Ensign John Lenci. (National Archives and Records Administration, Records Group 26 Entry 26C)
Click to Enlarge.

123. The methodical hand calculations required during the April 10th 1942
 compass calibrations
(National Archives and Records Administration, Records Group 26 Entry 26C)

We see that the April 1942 compass calculations took place at sea off the coast of Maine near Outer Green Island which is one of the many islands of Casco Bay. The notes from the Coast Guard District Compass Adjuster tell us that the Pequot’s gyrocompass was used as the reference during the calibrations. The Compass Adjuster pointed out that laying the metal cable from the Pequot’s hold could cause magnetic deviations and effect the accuracy of the binnacle. “The steering compass should be watched for changes in deviations with distribution of cable, necessitating constant check.  No great dependence should be placed on deviation table.” This reinforces how critical the Pequot’s gyrocompass was to accurate navigation of the ship.

124. The records of Pequot's September 2nd 1943 compass deviation adjustments note that the ship did not have a Degaussing Coil installed.  Yet at the top of the Deviation Table column notations for the Standard Compass we see references to "DG OFF" and "DG ON". DG stood for Degaussing.
(National Archives and Records Administration, Records Group 26 Entry 26C)  Click to Enlarge.

Gyrocompass: In addition to the main compass binnacle, during WWII the Pequot's pilothouse was also equipped with a Gyrocompass, which was invented in 1908 the year the ship was built.  A Gyroscopic Compass uses a spinning gyroscope which, once calibrated, keeps the compass pointing not to the magnetic north, but to the Earth's true North. Once the rapidly spinning gyroscope inside the compass is set spinning, it remains pointing in the same direction, regardless of the ship's motion at sea.

125. In one of the few photos we have inside the Pequot's pilothouse, we can see a gyrocompass with a magnifier for the Quartermaster similar to the one on the bridge of the 1945 Victory Ship S. S. Lane Victory (V-794). (Centre photo courtesy Mike Luongo; left and right images 

126. Pequot Quartermaster Ozzie Frontel keeps a keen eye on the gyrocompass. (Mike Luongo)

127. A Marine Clinometer of the era.
 (Maine Maritime Museum)

In addition to the standing compass binnacle and the newer gyrocompass, Quartermasters in the Pequot's wheel house also used the ship's wheel which was hydraulically connected to the steering engine, a Rudder Indicator which let them know what angle the rudder was set at, an RPM gauge which showed the revolutions per minute of the two propeller shafts, a Fathometer to let them see the depth of water beneath the keel, and a Clinometer which indicated the degree of roll the ship was under which was critical in rough weather.  

Pelorus:   Both the port and starboard side flying bridges on Pequot were equipped with a pedestal mounted gyro-compass repeater that duplicated the direction reading indicated by the main gyrocompass in the wheelhouse through electrical signals. To take bearings on objects outside the ship, a Pelorus with movable sighting vanes was mounted on top of these compass repeaters to enable the ship’s navigator to obtain direct bearings of objects which could aid in navigation such as a distinctive land form or a lighthouse.  True bearings were read by observing the degree on the compass card that the crossbar of the sighting vane lined up with. Relative bearings could be read from an outer dumb compass ring on  the  repeater  stand.

128. One of the Pequot’s pedestal mounted gyrocompass repeaters with Pelorus in place. Note the electrical cable which connects this compass to the main gyro-compass on the bridge. (Mike Luongo) 129. Quartermaster 1st Class Chester I. Isaacson taking a reading with a Pelorus on the Destroyer Escort USS Hilbert (DE-72) during WWII. 
George D. McCarthy)
130. When not in use the Pelorus was removed and the compass was covered to protect it from the elements.
(Calamaio Family)

To accurately determine the Pequot’s position, the standard formula of time at speed equals distance was used to calibrate how far the ship had traveled on a given bearing. Early binnacles included a sand timer similar to an hourglass. By the 1940s highly accurate ship clocks were the standard in every wheelhouse.

131. A 1940s US Navy Bureau of Navigation
Mark I deck clock. (Savage and Polite’s Antique Clocks)
132. Referred to as Celestial Navigation, a sextant enables ships at sea to determine their location by ‘fixing” their position from the sun, the moon, a planet, or a star and their angle above the visible horizon at certain times of the day or night.
(NOAA photo)

Quartermaster Lou Carhart tells us that the Pequot’s officers were responsible for all navigation calculations, plotting the ship’s course and maintaining the deck log entries. Quartermasters assisted with taking star or sun sightings off the horizon using a sextant, but primarily were responsible for keeping their attention focused on the bridge gyrocompass and keeping the ship on a given bearing.

Ship navigation was, and continues to be, a very complicated science where a number of elements all must be factored in using a variety of calculations and tools such as the use of a Maneuvering Board which is used for solving relative motion problems.  Bearing and distance marks from the center of the board and scales at the sides, allow quick and easy plotting of course and speed vectors to quickly determine and calculate a course bearing and a speed in knots to intercept, or avoid, another vessel.    

133. The Maneuvring Board was first established in 1920.  It uses a polar coordinate system that is divided into 360 units or degrees and a series of concentric circles which relate to speed in knots. Scales on the side of the diagram can be used to determine relative or actual speed and distance. (Defense Mapping Agency) 134. Various rulers, dividers, protractors, and other plotting tools were used with the Pequot’s nautical charts to calculate navigation solutions. Here we see a modern navigator’s “tool pack” using the same devices common on the Pequot more than 65 years ago. (Starpath Corp.)

Pequot Quartermasters Carhart, Simmons, Livingston and others all went through extensive training to obtain their rating where they had to learn that a ship’s speed was measured in knots which equal 1.151 nautical miles per hour, and that a nautical mile was equal to 1.15 statute miles on land.  Most importantly they had to gain the skills to handle the ship’s wheel and be able to respond to cross winds, heavy seas, and the techniques required for tight maneuvering especially during cable laying operations.

Even though today satellite generated GPS signals are used extensively for maritime navigation, ships still routinely use compass bearings and the earth's magnetism to set their course.

Every effort has been made to trace and acknowledge copyright. The authors would welcome any information from people who believe their photos have been used without due credit. Some photos have been retouched to remove imperfections but otherwise they are true to the original.


If you have comments or queries specifically about the Pequot or her Escort Ships, please contact
 Chip Calamaio, Phoenix, Arizona, USA. (H) 602-279-4505.

Click here to go to the Pequot Main Page.

Research and design: Chip Calamaio and Richard Walding