A closer look
When a massive military destroyer or civilian oil rig is heavily damaged at sea, traditional tugboats lack the structural strength to tow them to distant specialized repair yards. Engineers developed heavy-lift semi-submersible vessels that intentionally flood their massive ballasts to sink deeply beneath the ocean surface. The injured vessel is carefully floated directly over the submerged deck, and the massive transport ship dramatically rises, lifting the entire craft completely out of the water.
