War on the Rocks – In 1944 U.S. military planners drafted a plan to invade Taiwan: Operation Causeway. The plan was ultimately rejected by senior leaders due to the high costs and risks relative to alternatives for advancing against Tokyo. Analyzing Causeway provides a historical baseline against which to assess the enduring challenges of joint forcible entry operations, particularly those executed from the sea. Put simply, crossing a contested sea only to fight on complex, canalizing terrain against a deliberate defense-in-depth makes amphibious assault in Taiwan a more complex operation than even the famed 1944 Operation Overlord — the D-Day landings. A mix of Taiwanese defense planning and the reality of modern battle network competition compound these challenges, making an invasion likely harder in 2022 than in 1944.