U.S. Mail Steamship Company was a company formed in 1848 by George Law, Marshall O. Roberts and Bowes R. McIlvaine to assume the contract to carry the U. S. mails from New York City, with stops in New Orleans and Havana, to the Isthmus of Panama for delivery in California. The company had the SS Ohio and the SS Georgia built in 1848, and with the purchased SS Falcon in early 1849 carried the first passengers by steamship to Chagres, on the east coast of the Isthmus of Panama. Soon the rapid transit time the steamship lines and the trans isthumus passage made possible when the California Gold Rush began made it a very profitable company.
When in 1850 the Pacific Mail Steamship Company established a competing line to the U.S. Mail Steamship Company between New York City and Chagres, George Law placed an opposition Pacific Line of steamers (SS Antelope, SS Columbus, SS Isthumus, SS Republic) in the Pacific running from Panama to San Francisco. In April, 1851, the rivalry was ended when an agreement was made between the companies, the U.S. Mail Steamship Company purchased the Pacific Mail steamers on the Atlantic side (SS Crescent City, SS Empire City, SS Philadelphia), and George Law sold his ships and new line to the Pacific Mail. Law went into partnership with William Henry Aspinwall to develop the Panama Railroad in 1852.
In 1852 George Law had a dispute with the Cuban Captain-general, the Spanish official was incensed because the purser of one of Law's vessels had published an offensive statement in a New York newspaper, and he refused entrance to any vessel having the purser on board. The American government refused to sustain Mr. Law in his determination to send the Crescent City to Havana with the purser on board, and withdrew the mail when he persisted. He nevertheless despatched the steamship, and the Captain-general failed to carry out his threat to fire on her.