Unskilled and semi-skilled workers who traveled frequently in search of jobs developed a network of acquaintances and contacts in Northern cities. By the 1850s, a travel circuit had developed. For East Coast black migrants, the circuit included Philadelphia, New York City, Providence (Rhode Island), New Bedford (Massachusetts), and Boston. Often a worker was enticed from one of these cities to another by favorable reports from a friend who had gone before.

Down South, slaveholders were ever vigilant in attempting to isolate their chattel from "Northern information," but generally they were unsuccessful. African-American institutions, particularly churches, always suspect as centers of subversion, were closely watched. Despite the slaveholders' best efforts, however, Southern black churches were an integral part of the interregional underground.

Even though Richmond's First African Baptist Church had a white minister (this was not an unusual situation; slaveholders hoped that white pastors could maintain control over their black congregations), its members kept in touch with those gone North through a clandestine mailing system based in the church. Several who had fled from bondage wrote back to their former comrades, giving information to help others follow their example. Messages and letters were brought to the church and distributed to enslaved and free blacks in the city. The system was shut down in the mid-1850s, after local slaveholders discovered it.

The efficiency of the underground network is exemplified by the case of Henry Williams, who escaped from slavery in Louisiana in the 1830s and traveled to Cincinnati, where he worked, maintained his freedom for a number of years, and met and married a woman from another town. Members of his church who knew that Williams was already married, and that his wife, still in bondage, was living in New Orleans, were outraged. They charged him with bigamy and desertion. The congregation demanded a signed release from her before they would sanction his new marriage. Henry faced a grave problem. How could a fugitive in Cincinnati contact his first wife, who was enslaved in New Orleans, to obtain a signed document? The underground communication network was the answer. A boatman who regularly traveled to New Orleans found the first Mrs. Williams and secured her "X" on the paper as well as her enthusiastic support for dissolving the marriage. The church then recognized Henry's second nuptials.

Black seamen and boatmen were vital message carriers. The tradition of African-American sailors dates back to colonial times when they manned whaling ships and oceangoing merchant vessels as well as riverboats. In seaport and river port cities such as Boston and Cincinnati, the water routes offered an important source of income for African Americans.

Free Sailors and the Struggle with Slavery , Chapter 7 from Black Jacks: African American Seaman in the Age of Sail by W. Jeffrey Bolster

These mariners traveled frequently and were well versed in what one historian referred to as "travel craft" - the ability to seek out those with information vital to the survival of a black traveler in strange and possibly hostile places. Despite the efforts of authorities, many free sailors from the Northern states, the West Indies, and England came ashore and spent time between voyages in black communities in Southern ports. Some slaves also crewed on riverboats or coastal vessels. Contact between free and enslaved African Americans was thus relatively easy, despite white Southerners' fears that it threatened their efforts to keep their bondspeople in ignorance. Seamen were pivotal to the operations of the interregional communication system.

	Report on the Deliverance of Citizens Liable to be Sold as Slaves by Massachusetts General Court. Special Committee on Deliverance of Citizens Liable to be Sold as Slaves.
	We Best Can Instruct Our Own People: New York African Americans in the Freedmen's Schools, 1861-1875 from Afro-Americans in New York Life and History, vol. 12, no. 1 (January 1988) by Ronald E. Butchart

Free African Americans and fugitives in the North depended on the sailors to bring information about family and friends whenever they came north and to carry news back to the Southland. One Cincinnati woman kept in touch with her enslaved mother for more than three decades through messages smuggled by black boatmen. During those years she consulted her mother about her choice of a husband and informed her of the birth of her children. In 1843, the news of her grandchild's enrollment at Oberlin Collegiate Institute reached the proud grandmother in a Mississippi slave cabin, bound in body, she reported, but free in spirit.