• The US Navy developed a $50 million stealth surface vessel that was never put into operational use.

• The Sea Shadow's angular surfaces inspired the design of the Zumwalt-class stealth destroyers.

• Its influence also lives on in a new catamaran vessel designed for near-shore operations.

The Cold War was a golden age for stealth technology as the US military heavily invested in advanced systems and capabilities to get the upper hand over the Soviet Union.

Driven by the Soviet Union's advancements in radar and missile systems, the US military moved beyond just reducing radar visibility to designing fully radar-evading aircraft like Lockheed Martin's F-117 Nighthawk, the first operational stealth fighter.

But the US Navy sought to get eyes in the water as well, attempting to create the first stealth vessel that was undetectable by radar and sonar. The Navy never found a use for the one-of-a-kind vessel, whose design was ahead of its time and informed the creation of the Zumwalt-class stealth destroyers.

Its influence also lives on in a new catamaran vessel designed for near-shore operations.

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Stealth submarine to surface ship

Ben Rich, then the director of Lockheed's Skunk Works, decided to apply the F-117's stealthy coatings and angular shaping to a submarine.

Rich and his Skunk Works team — the industry leaders in stealth design — developed a small-scale model of a submarine dubbed the Sea Shadow to test in a sonic chamber. They found that the angular design of the cigar-shaped hull bounced sonar signals away from the vessel and muffled sounds it emitted from the crew and engine.

Trial and error

However, the Defense Department didn't find a need for underwater stealth craft, prompting Rich to adapt the design into a Small Water Area Twin Hull, a catamaran-style surface vessel designed to be stable and fast in rough seas whose futuristic design looked unlike anything else in the US fleet.

The Pentagon expressed interest in Rich's modified stealth surface vessel model, authorizing a $50 million contract through the Defense Advanced Research Projects Agency to Skunk Works to "test the effects of stealth shaping and coatings on surface vessels and effects of seawater on radar absorbing iron ferrite coatings," according to Lockheed Martin.

Top secret development

The Soviet Union's network of reconnaissance satellites could expose the positions of the US Navy's surface fleet. Drawing inspiration from the Nighthawk, the Sea Shadow incorporated sharp angles and flat surfaces of 45-degree angles to reduce the ship's radar visibility and avoid detection.

The stealth concept was tested in a 100-by-80-foot plastic swimming pool in Death Valley, California, using a simulated Soviet radar satellite. The successful test earned the project more funding to develop a prototype of the Sea Shadow.

Developed under strict secrecy, the Sea Shadow was constructed modularly, building smaller sections of the ship before they were taken to a submergible barge in California to be fully assembled.

The 164-foot vessel could accommodate a four-man crew consisting of the commander, helmsman, navigator, and engineer. The diesel-electric propulsion system allowed the vessel to reach speeds of up to 15 knots, or about 17 miles per hour.

Failure to launch

The Sea Shadow prototype was designed to test the application of stealth technology at sea, exploring how its stealth capabilities would perform in real-world conditions.

But the stealth ship was a one-off prototype with limited capabilities, and its odd, unconventional design was highly specialized, making it less practical for general use. Without the flexibility or features of the other multi-role vessels in the Navy's fleet, the Sea Shadow never saw use.

After nearly three decades sitting in storage at a private shipyard in San Diego, the Navy offered the Sea Shadow to museums for free, but there were no takers. Instead, it was sold at a 95% loss in 2012 — the highest bid amounting to $2.5 million — and was dismantled and scrapped.

Lasting legacy

Even though the prototype itself didn't fit into the Navy's evolving needs, it did provide valuable insights into adapting stealth technology for the sea. The lessons learned from Sea Shadow contributed to more advanced stealth ships and systems, like the Zumwalt-class destroyers.

While the expensive Zumwalt class has long struggled to find a suitable mission and weapons, they featured similar stealth characteristics to the Sea Shadow, like low radar cross-sections and angular shapes, to achieve greater survivability and effectiveness in modern naval warfare.

General Dynamics GHOST vessel

The Sea Shadow's design also has similarities with a new vessel. Developed by General Dynamics, the GHOST is an uncrewed vessel designed for coastal defense, special operations, and anti-piracy patrols. It can raise or lower its wings for low visibility, high speed, or stability.

The 62-foot drone has a shallow four-foot draft for coastal operations, and its hybrid turbine-and-electric drive allows the vessel to reach speeds of up to 32.5 knots, or about 37 mph. A General Dynamics brochure said it has two "stealth" modes.

Not only can the GHOST be modified physically to fit the mission at hand — like carrying missiles or ferrying 16 Navy SEALs — but it can also be operated by a pilot and navigator onboard, controlled remotely, or programmed as an autonomous platform.

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