Why port destruction could outlast the bombing campaign

Which ports were most heavily destroyed during the Second World War, and why did some remain unusable until after it?

German and Japanese ports are nominated, especially Hamburg, where dockside rubble entered the waterways; the exchange does not establish a definitive ranking or restoration timetable.

German and Japanese ports are nominated as some of the most heavily damaged in the Second World War. Hiroshima and Nagasaki are suggested first, before Hamburg is raised as another example. In Hamburg, collapsed dockside structures put rubble into the waterway, damaging access as well as the buildings around it. A suggestion that the bombing deliberately sought that effect is rejected: the dockside collapse is described as an unintended consequence. No comparative damage figures or reopening dates are given.