In the case of United States et al. v. Seatrain Lines, Inc., 1946, the U.S Supreme Court was tasked with determining whether or not Seatrain Lines had violated antitrust laws by acquiring a fleet of tankers from the government during World War II and using them for commercial purposes post-war. The government argued that this acquisition gave Seatrain an unfair advantage over competitors who did not have access to such resources, thereby violating antitrust regulations designed to maintain fair competition in commerce. However, Seatain countered that they were merely taking advantage of a business opportunity presented by war surplus sales and their actions did not constitute anti-competitive behavior. The Supreme Court ruled in favor of Seatrain Lines, stating that while it is true they acquired these vessels at less than construction cost due to wartime circumstances; there was no evidence suggesting any intent on part of Congress when selling these ships after war's end to restrict their use in domestic trade or limit competition within industry. Therefore, no violation occurred as per Sherman Act which prohibits monopolistic practices.

The dissenting opinion in the case of United States et al. v. Seatrain Lines, Inc., argued that the majority's decision was inconsistent with previous rulings and interpretations of antitrust laws. The dissenters believed that the acquisition by Seatrain Lines, a water carrier company, of two railroad companies did not violate antitrust laws because it would not result in undue concentration or monopoly power within their respective markets. They pointed out that both railroads were financially struggling and without this merger they might have ceased operations altogether which could potentially reduce competition even more significantly than if they merged with Seatrain Lines. Furthermore, they contended that this merger could actually increase competition by providing an alternative to other dominant carriers in these markets rather than reducing it as suggested by the majority opinion.