The US Defense Advanced Research Projects Agency (DARPA) is investigating a new approach to underwater construction that could allow robots to 3D print concrete directly on the seafloor. The proposed technology would use locally available ocean water, sand, and clay to construct or repair critical maritime infrastructure, potentially reducing the need to transport large quantities of conventional construction materials.
DARPA is seeking assistance from industry and academic researchers to overcome what it describes as major limitations in current underwater construction techniques. The research would focus on advanced robotic and maritime construction systems capable of operating in shallow coastal environments as well as at depths of up to 100 meters.
The long-term ambition is to establish the technology needed for a fully autonomous construction platform capable of operating in deeper waters. Such systems could potentially build and repair ports, piers, seawalls, and artificial reefs. They could also be used to reinforce areas surrounding underwater oil and gas pipelines and protect subsea telecommunications cables, which are increasingly important pieces of global infrastructure.
A central part of the proposed research involves adapting construction materials to local environmental conditions. Instead of relying entirely on transported cementitious materials, robotic systems could analyze available sediments and seawater and determine the most effective combination for producing printable concrete. Artificial intelligence could play a key role by evaluating local sediment characteristics and adjusting material mixtures according to conditions at each construction site.
The concept reflects the US military’s broader interest in autonomous systems. In recent years, military researchers have explored autonomous aerial and ground vehicles for surveillance, logistics, combat support, and casualty evacuation. The military has also experimented with 3D-printed structures on land. Taking robotic construction underwater, however, introduces an entirely different set of engineering challenges.
Underwater concrete construction is already possible, but existing techniques can require specialized machinery, extensive logistical support, and the transportation of construction materials to remote locations. According to DARPA, these approaches can be slow, expensive, and environmentally disruptive, limiting their practicality for rapidly deployed military operations.
Port and marine facilities
Maritime infrastructure is particularly vulnerable to deterioration. Continuous exposure to saltwater, humidity, storms, wave action, and corrosion can gradually weaken ports, piers, seawalls, and other structures.
These facilities are also strategically important, functioning as transportation hubs, logistics centers, and naval installations during both peacetime and military operations.
The condition of some US maritime infrastructure has raised concerns for years. Government assessments have previously highlighted aging military seaport facilities, while more recent evaluations of Coast Guard infrastructure have identified extensive maintenance problems.
A report released last year found that roughly 45% of Coast Guard facilities, including piers and mooring structures, had exceeded their expected service lives.
DARPA is also pursuing research into another side of the problem: predicting how concrete structures deteriorate over long periods. A separate program is investigating methods for forecasting the performance and failure of concrete infrastructure, including facilities such as aircraft runways.
Existing testing methods can measure concrete strength, but DARPA argues that they do not adequately reproduce the complex combination of environmental stresses, including heat and humidity, that structures experience in the real world.
The agency has been exploring unconventional approaches to infrastructure repair for several years. In 2023, DARPA awarded $10 million to researchers at the University of Colorado for a nearly five-year project examining the possibility of developing self-healing concrete.
The research, known as RC-REVIVE, investigates whether damaged infrastructure such as airfields, missile silos, and naval piers could repair themselves using systems inspired by biological networks.
The researchers are studying how networks of cracks inside concrete might serve as pathways for delivering nutrients and microorganisms capable of initiating repair. The concept draws an unusual but increasingly influential parallel between biological systems and engineered structures.
Offshore infrastructure
DARPA’s underwater 3D-printing initiative takes this broader ambition in another direction. Rather than simply designing stronger concrete or developing materials that can repair themselves, the agency is exploring whether autonomous machines could construct and maintain infrastructure in difficult environments with minimal human intervention.
If DARPA’s underwater 3D-printing initiative operation succeeds, the technology could redefine how vulnerable maritime structures are built, repaired, and maintained, turning the seafloor itself into part of the construction supply chain.
