Major construction at three of China’s large man-made islands in the disputed South China Sea is wrapping up, allowing Beijing to deploy fighter jets and mobile missile launchers to the area at any time, a think tank said Monday.

The building of military and dual-use infrastructure on the so-called Big 3 islands in the contested Spratly chain — Subi, Mischief, and Fiery Cross reefs — is in the final stages, with the naval, air, radar and defensive facilities largely complete, according to the Center for Strategic and International Studies’ Asia Maritime Transparency Initiative (AMTI).

All three islands boast hangers that can accommodate 24 fighter jets and four larger planes, including surveillance, transport, refueling or bomber aircraft. Hardened shelters with retractable roofs for mobile missile launchers have also been built on the islands.

China has also constructed significant radar and sensor arrays on all three islands, positioning them close to point defense structures to provide protection against air or missile strikes.

The think tank’s analysis of satellite images offers some of the most conclusive evidence that, contrary to Beijing’s assertions, China has continued to militarize the waters as it seeks to reinforce effective control of much of the waterway, through which $5 trillion in trade passes each year. The Philippines, Vietnam, Malaysia, Taiwan and Brunei also have overlapping claims.

China has built seven man-made islets in the hotly contested Spratlys, with three boasting military-grade airfields — despite a 2015 pledge by Chinese President Xi Jinping not to further “militarize” them.

“China’s three air bases in the Spratlys and another on Woody Island in the Paracels will allow Chinese military aircraft to operate over nearly the entire South China Sea,” AMTI said in the report. “The same is true of China’s radar coverage, made possible by advanced surveillance/early-warning radar facilities at Fiery Cross, Subi, and Cuarteron Reefs, as well as Woody Island, and smaller facilities elsewhere.”

China has maintained HQ-9 surface-to-air missile systems on Woody Island in the South China Sea’s Paracel chain for more than a year and has deployed anti-ship cruise missiles to the island on at least one occasion, the report noted.

Experts have said that deployment could be a blueprint for how China will proceed with its Spratly facilities.

“Building a network of outposts in the South China Sea is a strategically assertive way to tilt the regional military balance in China’s favor,” according to a report released last year by Australia’s Lowy Institute think tank entitled “Shifting Waters: China’s New Passive Assertiveness in Asian Maritime Security.”

“These strategic outposts will permit Beijing to enhance its power projection capabilities and establish anti-access zones right across the South China Sea,” the report said. “China will be able to extend the range and endurance of military and coast guard patrols; forward deploy air force, navy, and coast guard assets; and conduct aerial patrols over disputed waters, possibly in support of a future ADIZ (aid defense identification zone).”

The same report also said that a combination of ground-based radar facilities, air defenses, anti-ship missiles and forward-based fighter jets would facilitate the development of “mini-denial zones” extending southward from China’s Hainan Island that it could use to effectively chase the U.S. Navy out of the waterway.

Monday’s revelations of the near-complete construction at the three islands in the Spratlys comes ahead of plans by Japan to dispatch its largest warship on a three-month tour through the South China Sea beginning in May.