In fact, the story is even a little more complex than Martin Cox's wonderful web site lets on. For not only are IMM and United States Lines Company one and the same, but International Navigation Co., which operated the American Line, is also the same company, in an earlier incarnation. Based on the sources I have at my fingertips, I'm 95% certain that the following is correct; a review of the corporate records of the New Jersey Secretary of State, which I'm in the process of trying to arrange if the records go back far enough, would clinch it.
Originally known as International Navigation Co., Inc., a New Jersey corporation headquartered in Philadelphia, the company ran the American Line, which operated St. Louis (
http://www.greatships.net/stlouis.html) and St. Paul (
http://www.greatships.net/stpaul.html) for their entire careers (except for their military service). In 1902, when J. P. Morgan's shipping trust was created, International Navigation was the corporate vehicle by which this was accomplished. The company was recapitalized and, in October 1902, renamed International Mercantile Marine Co. Its state of incorporation remained New Jersey, but its corporate offices were later moved to New York City.
Leviathan, of course, began her career as Hapag's Vaterland; see
http://www.greatships.net/leviathan.html. After World War I, she was allocated to the United States as a war reparation and initially intended for IMM. That plan, though, was effectively killed by William Randolph Hearst, so the ship, renamed Leviathan, was placed in United States Lines (USL) service instead.
At first, USL was operated by the United States Shipping Board; later, it was turned over to a Delaware corporation called United States Lines, Inc., which is the Chapman-controlled company Martin refers to. This company, though, defaulted on its obligations to USSB, and in 1931, USSB took back control of its ships from the Chapman company. (Martin has this worded wrong on his page, I think. He says that Chapman foreclosed on USSB, when in fact it was the other way around: Chapman's USL defaulted and USSB foreclosed on it. I'll contact him about this.) A Nevada corporation, also called United States Lines, Inc., was then created to run USL and IMM was one of the owners of this corporation. IMM gained full control of USL on 5 July 1934; by then it owned 85 per cent of the common stock and 60 of the preferred stock of the Nevada corporation. Within two months, Leviathan was laid up for the last time, but for this brief time she was in effect owned by IMM, although operated by Roosevelt Steamship Co., which operated USL and acted as its sales agent until the end of 1934.
Finally, in May 1943, the Nevada corporation was merged into IMM, which still existed as a New Jersey corporation under the original International Navigation Co. corporate charter. At the same time, IMM changed its name to United States Lines Company, which is how the company was formally known for the remainder of the time that it operated USL, including the years when SSUS (
http://www.greatships.net/unitedstates.html) was built and in service.
International Navigation ... International Mercantile Marine ... United States Lines Co. The same company, albeit at different times, with different names and different corporate structures.
Sources: Vail's The American Peril; Flayhart's The American Line; Bonsor's North Atlantic Seaway.
MAB