Vietnam now has two airstrips in the Spratly Islands—but it may not be long until it gets another.

As reported October 25 by Radio Free Asia, Vietnam has begun laying down a runway on Barque Canada Reef. The area currently being prepared for paving is approximately 8,000 feet long—twice the length of Vietnam’s existing runway on Spratly Island and sufficient for most aircraft to take off and land at sea level. This length could also be extended even further given that the artificial landmass at Barque Canada now measures over 14,000 feet. In either case, the runway significantly expands Vietnam’s options for deploying combat aircraft to the Spratly Islands.

But Barque Canada may not be the only runway Hanoi has planned for the Spratlys. The western end of Pearson Reef, which was previously host only to a small Y-shaped concrete structure, has been rapidly expanded in recent months and brought to a conspicuous length of 8,200 feet. With work now beginning to fill in this extended area, it would be unsurprising to see another runway materialize at Pearson.

Likewise, the formerly miniscule outpost on Ladd Reef has also been extended to a length of 8,000 feet in recent months. Unlike Pearson, current structures in the center of the landmass would seem to preclude the installation of continuous runway along its length for now. But the scale and shape of the developing landmass warrants further attention.

Alongside these developments, signs of potential military structures have emerged across several features. New formations of berms encasing six protected areas are visible in recent imagery of Barque Canada Reef, Central Reef, Tennent Reef, Namyit Island, South Reef, and Ladd Reef. Given the coastal orientation of most formations, it’s possible these areas could be intended to house anti-ship artillery or missile platforms.

Other notable expansions include Tennent Reef, where the main landmass on its eastern side is being connected to the smaller outpost on its western edge. This extended land bridge creates another area with runway potential along the southeastern edge, which has room to be developed into 10,000 foot straightaway. South Reef has been expanded northward with a land area that extends 3,000 feet northward. And Alison Reef, which previously had no land area at all, has received a small parcel of it around one of its three concrete outposts.

Three years from when it first began, Vietnam is still surprising observers with the ever-increasing scope of its dredging and landfill in the Spratly Islands. Its progress in the last five months suggests that Hanoi is determined to maximize the strategic potential of the features it occupies. With dredging still beginning at new reefs and existing work growing in unexpected directions, it remains difficult to say when the expansion will end—and what new capabilities Vietnam will have once it has.