VietnamвЂ™s reclamation work remains modest by Chinese standards, however.

Regional military attaches say VietnamвЂ™s main holdings are well fortified, some with tunnels and bunkers, appearing geared to deterring easy invasion. The Asia Maritime Transparency Initiative, run by the CSIS, says Vietnam has added about 120 acres (49 hectares) of land to its South China Sea holdings in recent years. Taiwan also claims both but its position is historically aligned with BeijingвЂ™s. Vietnam has emerged as ChinaвЂ™s main rival in the South China Sea, actively asserting sovereignty over both the Paracel and the Spratly groupings in their entirety and undergoing its own naval modernisation. вЂњWe encourage all claimants to take steps to lower tensions and peacefully resolve differences.вЂќ вЂњWeвЂ™ve consistently warned that reclamation and militarisation in contested areas of the South China Sea will risk driving a destabilising and escalatory trend,вЂќ she said. The United States has repeatedly called on claimants to avoid actions that increase tensions in the South China Sea, through which around $5tn (ВЈ3.97tn) in world trade is shipped every year.ДЄ spokesperson for the US State Department, Anna Richey-Allen, said it was aware of reports of reclamation work by Vietnam and said the United States regularly raised concerns about such activity by claimants. Vietnam said 64 soldiers were killed as they tried to protect a flag on South Johnson reef вЂ“ an incident still acutely felt in Hanoi. Vietnam has long been fearful of renewed Chinese military action to drive it off its 21 holdings in the Spratlys вЂ“ worries that have escalated amid BeijingвЂ™s buildup and its anger at the recent Philippines legal action challenging its claims.Д¬hina occupied its first Spratlys possessions after a sea battle against VietnamвЂ™s then-weak navy in 1988. вЂњVietnam knows it canвЂ™t compete with China but it does want to improve its ability to keep an eye on them,вЂќ Poling said.

Ladd could also theoretically play a role in helping to defend VietnamвЂ™s holding of Spratly Island, where a runway is being improved and new hangars built, he said. Rather than a reclamation and a base, it could be an attempt to simply boost access for supply ships and fishing boats. Greg Poling, a South China Sea expert at WashingtonвЂ™s Centre for Strategic and International Studies (CSIS), said it remained unclear how far the work on Ladd Reef would go. The vessels at Ladd Reef cannot be identified in the images but Vietnam would be extremely unlikely to allow another country to challenge its control of the reef. VietnamвЂ™s foreign ministry did not respond to a request for comment. Reuters reported in August that Vietnam had fortified several islands with mobile rocket artillery launchers capable of striking ChinaвЂ™s holdings across the vital trade route. вЂњTheyвЂ™re doing everything they can to fix any vulnerabilities вЂ“ and that outpost at Ladd Reef does look a vulnerability.вЂќ and they are rapidly improving their defences,вЂќ said Trevor Hollingsbee, a retired naval intelligence analyst with the Ministry of Defence. вЂњWe can see that, in this environment, VietnamвЂ™s strategic mistrust is total. While the purpose of the activity cannot be determined for certain, analysts say similar dredging work has been the precursor to more extensive construction on other reefs.

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