[Capt James F. Bradley Jr.] was at his office in Naval Intelligence one day at 3 a.m. when the St. Louis native began reflecting on his boyhood life on the Mississippi River. As he later told the authors, he recalled that the river beach was dotted with signs warning, “Cable Crossing — Do Not Anchor,” so a boater would not foul the cable.
At that point, he wondered if the Soviets did not have similar signs along their Arctic coasts to prevent their critical cables, including those used by the KGB and the Soviet Northern Fleet, from being damaged.
As a result of these ponderings, in 1971 the American submarine Halibut, with its periscope up, slowly and secretly traced the Siberian coast looking for telltale warning signs. The cable signs were found, and American divers put a tap at the bottom of the Sea of Okhotsk on Soviet communications.
https://stationhypo.com/2021/09/05/remembering-captain-james...