The Marines may be “the only branch adapting fast for the future” (“U.S. Defense After Ukraine,” Review & Outlook, March 8), but what future and how wisely? The military’s poor record of predicting the next war urges maintaining flexibility. This has long been a strength of the Marine Corps, which maintained itself for decades as a combined-arms force in readiness, rapidly deployable, balanced and able to organize for any mission. This has proved its worth to the nation at all levels of crisis and conflict.