Comment by floppydisk

As with all other Forward Operating Bases (FOB), it will face the same challenges as any island during conflict. If you can exhaust the island's supplies and constrict replenishment, the utility of the island diminishes. In the case of Diego Garcia, assuming a conflict with China, they lack the force projection capabilities to effectively shut down the flow of supplies to DG. (Assuming the US submarine force > chinese submarine force in capability). Their best bet would be to render it inert using cruise missile and non-nuclear ICBM strikes to disable the runways, mine the anchorages, and destroy the fuel supplies. Bonus points if they can sink ships in the lagoon.