DARPA Wants Robots to 3D Print Concrete Underwater for Military Ports

From Land Bases to the Seabed

The US military has already printed barracks, runways, and drone factories on land. Now DARPA wants to take the same idea underwater. The agency is soliciting proposals for the Trenton program, which aims to develop robots that can print concrete structures on the seafloor using nothing but local sediment and seawater.

On August 18, 2026, DARPA outlined the goal in a new solicitation: build a system that can construct or repair ports, seawalls, artificial reefs, and underwater cable protection in shallow water and depths up to 100 meters. The idea is to cut the logistics chain that normally forces the military to ship cement, aggregate, and heavy equipment to damaged coastal sites.

Why Underwater Concrete Printing Matters

Current underwater construction is slow and expensive. Divers and cofferdams are often needed just to place concrete in a dry enough environment. That makes emergency repairs at remote or contested ports nearly impossible. A robotic printer that mixes and deposits concrete directly on the seabed could change the timeline from weeks to days.

The military has another reason to care. Around 45 percent of Coast Guard maritime facilities, including piers and moorings, are already past their expected service life according to a recent government report. In a conflict, those same ports would be prime targets. The ability to patch them quickly without importing raw materials would be a genuine logistics advantage.

What the Technology Needs to Prove

The Trenton program is not asking for finished products yet. Phase one is about proving that land-based 3D concrete printing can be adapted for underwater use. Researchers need to solve problems that do not exist on a construction site: preventing mix washout, controlling cure chemistry in cold saltwater, and building structures that stay put while waves and currents push against them.

DARPA also wants the system to avoid toxic additives. Since the whole point is to use native sediment, importing exotic binders defeats the purpose. The program specifically asks for formulations that rely on seawater and seafloor material, with AI helping to adjust the mix for local conditions.

Parallel Work on Self-Healing Concrete

This is not DARPA's only bet on smarter cement. In 2023 the agency gave the University of Colorado $10 million for RC-REVIVE, a project that embeds biological networks in concrete so cracks can heal themselves like living tissue. That work focuses on land-based infrastructure, but the same materials science could eventually feed into underwater repairs.

From Military to Civilian Use

If Trenton works, the applications go well beyond defense. Coastal cities facing rising sea levels could print erosion barriers without trucking in concrete. Offshore energy platforms could repair foundations on site. Environmental restoration teams could build artificial reefs without dumping foreign materials into marine ecosystems.

The solicitation makes clear this is a long-term bet. DARPA expects performers to demonstrate printable chemistries and subsystems, not a fully autonomous fleet of seabed construction robots. But the direction is obvious: the military wants additive manufacturing to work anywhere, including a place where most 3D printers would short out in seconds.

Read the full DARPA Trenton program outline and Business Insider's coverage for more details.