This book in an index of 18,354 names compiled from original applications for Seamen's Protection Certificates (SPC) filed at the Port of Philadelphia between 1824 and 1861. As a group, seamen were often missed at census time; consequently the SPC application may be the only record available for many 18th-century persons who served in the American merchant marine. The index gives the name of the seaman, date of application, age, race, and state or country of birth. Additional information can be found in the SPC applications themselves, as they contain references to the seaman's place of birth, physical features, and, where applicable, place of naturalization or facts concerning manumission.