China deploys 42 ships and hundreds of oceanic sensors to prepare for submarine warfare against the US Navy.

China deployed a network of 42 research vessels and hundreds of oceanic sensors to map subsea environments across the Pacific, Indian, and Arctic oceans, building a detailed operational dataset to support submarine warfare against the U.S. Navy.

The multi-year campaign combines seabed mapping and real-time environmental monitoring to enhance underwater navigation, concealment, and sonar performance in strategically contested maritime zones. Spanning across key chokepoints and naval corridors near Taiwan, Guam, and the Malacca Strait, this new capability directly strengthens China’s anti-submarine warfare and operational framework by enabling precise prediction of sonar conditions and optimized submarine operations in regions used by US and allied naval forces.

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These data enable submarines to navigate safely, remain concealed using terrain and acoustic conditions, and detect or evade adversary submarines more effectively, through precise knowledge of how sound propagates in specific underwater conditions. (Picture source: U.S. Navy)

On March 24, 2026, Reuters announced that China’s ocean-floor mapping activity across the Pacific, Indian, and Arctic oceans reflects a coordinated, multi-year effort to generate detailed knowledge of subsea conditions directly usable for submarine operations against the U.S. and allied navies. The large-scale campaign involves at least 42 research vessels tracked over more than five years, supported by hundreds of deployed sensors positioned across key maritime corridors. These operations focus on areas where submarine transit, detection, and interception are operationally relevant, including chokepoints and routes near major naval facilities. The continuously updated environmental database includes seabed terrain, water temperature, salinity, and current patterns, all of which directly affect submarine movement and sonar performance.

Civilian research missions such as climate studies and seabed sampling are conducted in parallel, but the same data is directly usable for military purposes. This reflects an integrated approach within China combining oceanography, mapping, and surveillance to support undersea operations. The resulting datasets provide both static terrain information and dynamic environmental variables, which are essential for underwater warfare. A representative example is the Dong Fang Hong 3, a general-purpose scientific research vessel that conducted repeated survey missions between 2024 and 2025 in three distinct operational zones: waters near Taiwan, the vicinity of Guam, and strategic areas of the Indian Ocean.

In October 2024, the Chinese ship inspected seabed sensor systems near Japan capable of detecting underwater objects and returned to the same location in May 2025, indicating follow-up activity such as recalibration or data retrieval. In March 2025, it conducted dense survey tracks between Sri Lanka and Indonesia, covering approaches to the Malacca Strait. These operations align with key maritime routes used for energy imports and naval movement. The vessel’s repeated presence in the same regions suggests systematic mapping rather than exploratory deployment. Its missions included both climate-related research and deep-sea mapping functions. This dual-use profile, according to Reuters, is consistent across multiple vessels involved in the wider campaign. 

Survey techniques observed across the Chinese fleet rely on parallel track navigation, with ships moving in tightly spaced lines to ensure full seabed coverage and minimize gaps in collected data. This method produces high-resolution bathymetric maps, capturing depth gradients, seabed composition, as well as features such as ridges, slopes, and sediment layers. These elements directly affect submarine maneuverability and sonar reflection patterns. At least eight vessels have conducted dedicated seabed mapping missions, while ten others are equipped with mapping systems. This indicates that mapping capability is distributed across multiple ships rather than centralized. The repetition of survey patterns over the same areas allows for data validation and refinement over time.

As a result, the datasets evolve from basic charts into detailed environmental models of the seabed. The fixed sensor network complements vessel-based surveys by providing continuous monitoring of ocean conditions in specific locations across multiple regions. Deployments include seabed sensors, moored buoys, and subsea arrays positioned east of Japan, east of the Philippines, and around Guam in the Pacific. Additional arrays are located in the Indian Ocean near Sri Lanka and along the Ninety East Ridge. These systems measure temperature, salinity, and current patterns, as well as detecting subsea movement. The placement of sensors aligns with known submarine transit routes and maritime chokepoints.

Data collection is continuous, allowing the tracking of environmental changes over time rather than single-point measurements. This creates a persistent monitoring layer that extends beyond the limited duration of vessel deployments. Environmental data collected from these systems directly determines a submarine's sonar performance and underwater detection capability. Sound propagation is influenced by temperature gradients, salinity levels, and pressure conditions, which together shape how acoustic waves travel through water. Variations in these parameters create thermoclines and other layers that can refract or absorb sound. By combining seabed mapping with water-column measurements, it becomes possible for a country to model acoustic conditions with location-specific precision.

This allows the identification of zones where sonar detection ranges are reduced or enhanced. Such modeling supports both evasion and detection strategies in submarine operations. The ability to predict acoustic behavior in specific areas reduces uncertainty during undersea missions...or anti-submarine warfare. This data is also directly applied to submarine operations, where navigation, concealment, and survivability depend on accurate environmental knowledge. Submarines operating within a few hundred meters of the surface must account for terrain and water conditions to avoid detection. Bathymetric data allows vessels to use seabed features such as slopes or depressions for concealment.

At the same time, a better knowledge of thermal layers enables an optimized submarine positioning within acoustic shadow zones. These zones reduce the effectiveness of enemy sonar systems. Detailed environmental data also supports route planning for extended missions in contested areas. The result is increased operational flexibility and reduced exposure during deployment. The same datasets enhance anti-submarine warfare by improving detection accuracy and tracking capability. Sonar systems must be calibrated to local environmental conditions, and without precise data, detection ranges can vary significantly. With detailed measurements, sonar performance can be optimized for specific locations.

This increases the probability of detecting submarines operating within those environments. In addition, seabed mapping allows identification of likely transit routes based on terrain constraints. In short, this permits the placement by China of fixed sensors or monitoring systems in the most optimal positions. Persistent surveillance becomes possible in key maritime corridors, especially those used by the U.S. Navy. For China, such capabilities contribute to both defensive and offensive undersea operations. Geographically, China's undersea mapping activity is concentrated in areas with high operational significance for the U.S., including the First Island Chain east of the Philippines, waters near Taiwan and Guam, and even regions around Hawaii and Wake Atoll.

This must not be surprising, as these locations correspond to major U.S. military facilities and key naval transit routes. Additional mapping has been conducted between Sri Lanka and Indonesia, covering approaches to the Malacca Strait, an area as critical for maritime trade and energy flows as the Strait of Hormuz or the Panama Canal. Activity also extends into the Indian Ocean more broadly and toward Arctic waters west and north of Alaska. These regions could represent future operational areas linked to global shipping routes. The distribution of activity reflects a focus on both current and emerging strategic maritime zones following climate change.

Taken together, the Chinese mapping campaign and sensor deployments create a layered dataset covering seabed terrain and water-column conditions across multiple theaters. This dataset reduces uncertainty in submarine navigation and detection by replacing generalized ocean knowledge with location-specific data. The combination of repeated surveys and continuous monitoring provides both static and dynamic environmental information. This enables more predictable planning for undersea operations, including anti-submarine warfare.

Like many domains in China, the integration of civilian activity with military applications supports sustained data collection, which is an inescapable directive from the Chinese Communist Party that must be followed by every Chinese citizen and organisation. Over time, this approach builds a detailed operational picture of key maritime environments. The result is a shift toward continuous, data-driven undersea activity in strategically important regions for both the U.S. and China, as well as a force multiplier for the Chinese submarine force, which is expected to reach up to 80 units by 2035.

Written by Jérôme Brahy

Jérôme Brahy is a defense analyst and documentalist at Army Recognition. He specializes in naval modernization, aviation, drones, armored vehicles, and artillery, with a focus on strategic developments in the United States, China, Ukraine, Russia, Türkiye, and Belgium. His analyses go beyond the facts, providing context, identifying key actors, and explaining why defense news matters on a global scale.