Crane lifting was only one way to move a dock caisson. Pumping water out could give a sufficiently light caisson positive buoyancy. Tugs could then move the floating barrier clear of the entrance. This qualifies the earlier crane-based explanation: the handling method depends on whether the caisson can float once emptied.
Notable Point · 3:40:18-3:40:43
Moving a buoyant dock caisson with tugs
A caisson that becomes buoyant after pumping can be moved by tug, providing another method besides crane lifting.