When it comes to transporting large things at sea, sometimes the very best option is to move it in one piece. But what if that thing is an entire oil rig?
Enter the Heavy-Lift Ship: a specially designed vessel which can partially submerge to allow other ships, yachts, oil rigs and drilling platforms to float over its massive, flat cargo deck. The ship lowers itself into the water using a series of ballast tanks which can be flooded. Then, after the cargo has been floated over the deck, air is pumped back into the tanks and the massive ship lifts its cargo aboard.
Heavy-lift ships have been used to rescue two US warships, including the USS Samuel B. Roberts, which struck an Iranian mine in 1988, and the USS Cole which was attacked by suicide bombers in Yemen in 2000.
Launched in 2012, the Dockwise Vanguard is now the largest heavy-lift ship. At 902 feet long (275m) and 230 feet wide (70m) it can lift a staggering 120,000 tons.
The heavy-lift ship MV Mighty Servant 2 carrying the USS Samuel B. Roberts after it struck a mine in 1988.
How about carrying a whole stack of ships?
Dockwise Tern loading an oil platform.
MV Blue Marlin submerges its deck for loading.
MV Blue Marlin carrying the damaged USS Cole home from Yemen.
MV Blue Marlin with an oil platform on its deck.
MV Blue Marlin carrying the Sea-Based X-Band Radar as it enters Pearl Harbor, Hawaii. This is after completing a 15,000-mile journey from Corpus Christi, Texas, in 2006.