Since the mid-1970s the United States has advocated U.S.-European weapons procurement cooperation to promote increased NATO equipment rationalization, standardization, and interoperability (RSI). A comprehensive strategy including the collaborative development or codevelopment of weapon systems has been devised to facilitate transatlantic weapons procurement cooperation. This report examines three major European large aircraft codevelopment programs conducted between 1958 and 1974 to determine whether these programs achieved the benefits within Europe that U.S. advocates had hoped for. It also explores the European motivations and objectives for codevelopment; the effects of codevelopment on the rational management of transnational R&D funds and resources; the codevelopment program schedule, cost, and performance outcomes; and the prospects and desirability of U.S. participation in a future European large aircraft codevelopment program. Conclusions suggest that the transatlantic collaborative development of large aircraft would not be an effective strategy for augmenting NATO military capabilities and reducing overall NATO defense costs through increased equipment RSI.