From https://www.ancestry.com/c/family-history-learning-hub/naturalization:

Beginning on June 29, 1906, certificates of arrival were issued to prove a non-naturalized immigrant had met residency requirements. When an applicant filed a declaration of intent, the ship’s name, date, and port of arrival were given. That information was verified in passenger lists from that port, and a certificate of arrival was issued to be filed with citizenship papers. For people researching their family history, these records tend to be less common than petitions for naturalization and declarations of intent.