Aerial pictures taken by the US already show airfields and fortifications: on Fiery Cross Reef a 3,000m runway has been constructed that is capable of handling fighter jets. A second such airfield appears to be under construction on another island.
Wu Shicun, president of the Hainan-based National Institute for South China Sea Studies, is among those who believe Beijing may choose the militarisation route, stationing fighter planes and warships on the islands.
"If America only comes into the South China Sea this one time, then China might only take one-time action. If America decides to frequently enter this region, this will make China feel threatened . . . they will have a reason to militarise the islands in order to ensure their safety."
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Richard Bitzinger of the S Rajaratnam School of International Studies in Singapore concurs. "I don't think the Chinese need much excuse to militarise the islands," he says. "The escalation so far has been chiefly on their side. They will wait to see how often the US does this and for how long, and whether other countries, such as Japan, get involved."
Others see less bellicose outcomes. Gary Li of Beijing-based consultancy Apco Worldwide sees China finding a "face-saving and de-escalatory path" out of the confrontation — if the US makes no further incursions.
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"The islands are always going to be militarised to an extent. But the difference is whether there are 10 guys living in houses with stilts, or several hundred guys in reinforced bunkers with fighter planes," he said.
Much will hinge on the next US move and whether or not it targets other countries, which would demonstrate impartiality.
Paul Haenle, director of the Carnegie Tsinghua Centre in Beijing, says: "The fact that [the US] hadn't operated near the features in question since 2012, and are now doing so after a period of heightened tension in US-China relations over this issue, likely contributes to China's perception that the primary US goal here is to target them."