Immersed and floating tunnels are types of underwater tunnels: the former is buried in the bed of the waterway and the latter is not. Although the first floating tunnel has yet to be built, serious design efforts are well underway. Each type is fabricated in sections at a convenient location in the dry and then moved to its final installed location by floating at least part of the way. It is paramount that both types of structures are sufficiently resilient to preclude failure and subsequent catastrophic flooding whatever their imposed dynamic and other loadings. This paper examines these loadings and how these structures might meet their requirements for resilience within their respective transport systems. Because a risk of potential flooding exists, these requirements are somewhat different to those of land-based structures.