The Pequot's Indicator Loops in Action

This page provides more detail about the role of the U.S. Coast Guard Cable ship Pequot during World War II. The Pequot laid anti-submarine defences known as Indicator Loops in strategic harbors along the east coast of the US. This webpage provides examples of ships and "signatures" (paper charts) generated by the loops as each ship passed overhead.
 For this - with the help of Marty Dwyer - we have accessed WWII era indicator loop charts stored at the Waltham Massachusetts National Archives and Records Administration (NARA) Northeast Region repository.  For specific information on how to read loop charts and details on the equipment and physics associated with this technology see our Reading a Loop Signature Page. Our main page for the USCG Pequot provides extra details about the ship, its crew, its purpose as well as links to our other Pequot pages. For general information about indicator loops see Loops around the World.

The US Coast Guard Pequot. During WWII this cable ship laid top secret Indicator Loop cables to protect harbors from German U-boats. Her mission ranged from the ports of Virginia up to Argentia, Newfoundland. (Calamaio family).


Once the indicator loops installed by the Pequot to protect US harbors were functional the officers and specialists who constantly monitored this harbor defense technology routinely saw how the loops picked up and recorded the passage of US warships and merchant craft across the loops cables. The experience gained by loop technicians recording and analyzing the loop signature voltages generated by friendly US and Allied ships enabled them to keep a better eye out for German U-boats or other unidentified enemy ships.

Not only do these charts provide a record of US ship movements but they clearly illustrate how different size ships, traveling at different speeds over the indicator loops produced similar, yet different, electronic signatures. The presence of large surface craft was very clear while the signature of smaller ships and submarines was more subtle.

For illustration purposes we’ve provided a photo of the ships who generated these loop signatures and by using the “Time 1st Impulse” and “Time Last Impulse” on the charts we’ve calculated how long it took these ships to cross the three legs of the indicator loop when coming in and going out of port. You need to picture the chart paper moving downwards past the pen.

USS Chicopee

The oiler USS Chicopee (AO-34) was a workhorse of WWII and served as a supply tanker to support fleet and Atlantic convoy operations before being transferred to the Pacific theater in 1944. The ship’s missions took her to Iceland, Newfoundland, Gibraltar, Northern Ireland, Casablanca, and ultimately Tokyo Bay. (


USS Chicopee Inbound Crossed the loop in 5 minutes. Here we can see a full record of the ship’s passage from first to last impulse readings.

USS Chicopee Outbound

Crossed the loop in 5 minutes

USS Juneau

The Atlanta class light cruiser USS Juneau (CL-52) was on the East coast briefly before serving in the South Pacific in the battle of Santa Cruz Islands and the Naval Battle of Guadalcanal. She was sunk by a Japanese submarine with great loss of life including the five Sullivan Brothers. (


USS Juneau Inbound

Crossed the loop in 3 minutes

USS Juneau Outbound 

Crossed the loop in 2 minutes

Here we see that when the Juneau steamed out of harbor faster and crossed the loop a minute quicker than it did coming in the ship’s signature on the indicator loop chart was markedly different.

USS Massachusetts

Two months after she was commissioned South Dakota class battleship the USS Massachusetts (BB-59) crossed one of the Portland Maine indicator loops on July 14th 1942. (


USS Massachusetts Inbound

 Crossed the loop in 4 minutes

USS Massachusetts Outbound

Crossed the loop in 2 minutes

Even though the USS Massachusetts crossed over the loop cables in half the time going out as it did coming into harbor the sheer steel mass of this heavy battlewagon produced a very dense  signature when crossing all legs of the loop installation.

Submarine S-48

Submarine S-48  (SS-149) was an S-class submarine constructed in 1920 that served as a submarine and anti-submarine training ship out of New London, Connecticut and Portland, Maine during WWII. (US Navy Photo)


Submarine S48 Inbound

Crossed the loop in 2 minutes

Submarine S48 Outbound

Crossed the loop in 2 minutes

Compared to a large ship like the USS Massachusetts (above) we see the very thin signature of a submarine crossing the legs of an indicator loop within an identical 2 minute time span.  These short thin loop signatures which could signal the presence of a German U-boat are what everyone remained watchful for.

 USS San Juan

After being commissioned on February 28th 1942 the Atlanta class light cruiser USS San Juan (CL-54) completed shakedown runs in the Atlantic before departing on June 5th for service in the Pacific. During her May 1942 sea trials the San Juan crossed the indicator loops protecting Portland Maine.(  


USS San Juan Inbound

Crossed the loop in 3 minutes

USS San Juan Outbound

Crossed the loop in 4 minutes

Submarine S-20

Submarine S-20 (SS-125) February 2nd 1944.  This 1918 era S-class submarine was stationed out of New London, Connecticut  and served off New England throughout WWII including training duties at Casco Bay, Maine. (US Navy Photo)


Submarine S-20 Inbound

Crossed the loop in 2 minutes

Submarine S-20 Outbound

Crossed the loop in 2 minutes

USS Goldsbourgh

The narrow beam four stack destroyer USS Goldsbourgh (DD-188) crossed the Fort Williams “Able” Loop on November 28th 1943. This Clemson-class destroyer saw action and served with distinction in both the Atlantic and Pacific campaigns of WWII. (US Naval History and Heritage Command Photo)



USS Corry

The destroyer USS Corry (DD-463) led the 5,000 ship armada from England to Normandy for the invasion of France on June 6th 1944. While providing close in bombardment of German shore batteries above Utah Beach the Corry was hit by German artillery fire, broke amidships, and sank. Earlier in the war the Corry served patrol and escort duty along on the East coast and crossed the Portland, Maine loop cables. (US Navy photo)


USS Corry Inbound
Crossed the loop within 2 minutes

USS Corry Outbound
Crossed the loop within 1 minute

We can clearly see the difference in signature density when comparing the faster outbound readings with the slower readings when the Corry came into harbor.

USS Kilauea

The ammunition and supply ship USS Kilauea (AE-4) played a vital role in supplying Allied forces in the Atlantic and Pacific theatres during WWII as well as service during the Korean war and Vietnam conflict.  In May of 1942 while serving along the Atlantic seaboard and supplying the Argentia, Newfoundland base the Kilauea crossed the Portland Maine indicator loops. (US Navy Photo)

USS Kilauea Inbound

Crossed the loop in 3 minutes

USS Kilauea Outbound

Crossed the loop in 4 minutes

The density of the loop signature is seen in the Kilauea’s slower outbound passage over the indicator loop cables.

Research by Chip Calamaio and Richard Walding with Special Thanks to Marty Dwyer.

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.