Table of Contents As filed with the Securities and Exchange Commission on December 5, 2025. Registration No. 333-290011 UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, DC 20549 Amendment No. 2 To Form F-1 REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933 C3IS INC. (Exact name of registrant as specified in its charter) Republic of the Marshall Islands 4412 N/A (State or other jurisdiction of incorporation or organization) Puglisi & Associates 850 Library Avenue, Suite 204 Newark, Delaware ...

Table of Contents As filed with the Securities and Exchange Commission on November 3, 2025. Registration No. 333-290011 UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, DC 20549 Puglisi & Associates 850 Library Avenue, Suite 204 Newark, Delaware 19711 (302) 738-6680 (Name, address and telephone number of agent for service) Amendment No. 1 To Form F-1 REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933 C3IS INC. (Exact name of registrant as specified in its charter) Republic of the Marshall I ...