Last week, China's coast guard mounted what the Philippines called an "unusual" show of force at Second Thomas Shoal, a hotly disputed submerged reef in the Spratly Islands where Manila maintains a small outpost in the form of the rusting warship BRP Sierra Madre, grounded there in 1999 to anchor its territorial claim.

Artificial islands housing munitions and aircraft created in an attempt to lay claim to disputed islands vital for shipping

AMTI imagery shows Vietnam accelerating Spratly reclamation, surpassing 2,300 acres with new harbors and an airstrip.