Until 1838 the U.S. government lent railroads Army engineers to survey routes. Though not strictly regulators, these army engineers would consequently face powerful versions of the incentives that make regulatory capture a pervasive problem—including an intensified “revolving door,” the opportunity for institutional empire building, and a fertile ground for cognitive capture. Nevertheless, engineering officers would push to abolish federal railroad aid, succeeding by 1838. This article argues that they turned against railroad aid when the nation’s growing rail network revitalized long-standing republican hopes of replacing standing armies and fortifications with floating batteries and militias. Though this scheme was strategically quixotic, Jacksonian populism and fiscal retrenchment during the Panic of 1837 combined with the transportation revolution to make it appear a credible threat to the Corps’s institutional raison d’être—building coastal fortifications. Engineers thus turned against railroad aid to protect their core competency, highlighting underappreciated tensions between institutional and industry interests.