One version could be a floating airstrip platform for military purposes. It could 900 meters long. The US Navy Gerald Ford Super aircraft carriers are 330 meters long
The largest container ships are about 400 meters long.
The Prelude is an oil platform and it will be 488 meters long and displace 600,000 tons.
The Chinese platforms could be 400,000 to 1.5 million tons of displacement and could be 900 meters long.
DG's floating island designs are modular, being assembled from multiple semi-submersible hull sections. They would come in three sizes. The smaller island is 300 meters long and 90 meters wide, the medium sized island is 120 meters wide and 600 meters lond, while the larger island is 900 meters long and 120 meters wide. Assuming a hull draft of around 16 meters, full displacement of the islands could likely be around 400,000 and 1.5 million tons, respectively.
This JDG floating island island is even larger than the currently planned 900m long floating island. With a length of 2 kilometers (the cargo ship alongside it would be around 400 meters long), its large size is made possible by the modular construction of JDG's shipbuilding technology. The islands can also travel at speeds of up to 18 kilometers an hour.
Such giant bases could house battalions of marines and a wing of fighter/attack aircraft, and unlike fixed island bases, they can be redeployed away from enemy missiles.
SOURCES - Wikipedia, Popular Science