Sea Shadow: how the Stealth Bomber turned into a stealth ship
Sea Shadow on the water. Image from Lockheed Martin.
The Sea Shadow was a top secret military vessel built to test the limits of stealth technology and bring stealth fighter jet “invisibility” to the sea. Ben Rich was working at Skunk Works when he heard a company photographer complaining that something was wrong with his Polaroid camera as he tried to shoot a model of an F-117 stealth fighter. According to Lockheed Martin, Ben told him “Time out! There isn’t one thing wrong with your new camera.” The design of the F-117 from the shape to the coatings on the aircraft prevented the camera’s sonar-like focusing device from focusing for a clear photo. This event let Rich to dive into applying the technology of the F-117 to a submarine in order to avoid detection on sonar.
The F-117 Nighthawk was designed from the ground up to deflect radar waves by using surfaces that direct the radar away from detectors. The doors and panels have saw-toothed edges to also reflect radar. The surface is coated with a radar-absorbent material, or RAM, further reducing its detectability. This “Stealth Bomber” as it was often called, only operates at night just as testing for the Sea Shadow was always carried out under cover of darkness, according to Airforce Technology. The similarities between the aircraft and the vessel give away their relation as both were designed by Skunk Works.
“F-117A Nighthawk is an attack aircraft developed by Lockheed Martin.” Image from Airforce Technology.
How a submarine turned into a boat
Realizing he had something by bringing stealth aircraft technology to the water, Rich’s team purchased a model submarine and added faceted fairings for sonic chamber testing. In engineering, an improvement of one magnitude, or 10x, is considered a huge improvement and worthy of celebration. What they discovered was an improvement in sonar return of three orders of magnitude, 1000 times better with just a simple model. They got to work and the first design was cigar shaped like a normal submarine, but with angular outer surfaces like the F-117 to deflect sonar and dampen internal noise from the crew. Acoustic tests confirmed huge improvements in sound deadening, prompting Rich to approach a Navy captain at the Pentagon in charge of submarine research and development, according to Lockheed Martin. The captain was not convinced, worried about loss of speed even with the prospect of invisibility. Another Skunk Works engineer told Rich about a new naval ship design he had just seen, the Small Water Area Twin Hull (SWATH). This new vessel was quicker than a normal ship and very stable with its catamaran design, a nice match for stealth technology. After going back to Washington to talk with the Defense Undersecretary about the idea in a meeting that was supposed to be about the F-117, he was approved a contract through the Defense Advanced Research Projects Agency, or DARPA to work on the vessel.
A big threat to vessels at that time was Soviet satellite X-band radar, so Rich’s team used the flat angular design of the Nighthawk to deflect those signals. They confirmed their tests by putting the vessel in a 100 by 80 foot plastic swimming pool in a dry lake bed in Death Valley and using a test radar system similar to the satellite threat. The test was successful and the project joined the Ocean Division of Lockheed Martin.
How the Sea Shadow was built
Sea Shadow under construction inside HMB-1. Image from Maritime National Park Association.
To keep the project super-secret (even many military officers with top secret level clearance didn’t know about the construction of Sea Shadow), the ship was built completely inside a floating dry dock vessel called Hughes Mining Barge I, or HMB-1. According to Lockheed Martin, a four man crew built the ship in pieces before they were taken to the submersible barge and assembled. The modules were made by four different manufacturers to ensure no one company had a clear picture of the final product. According to Maritime National Park Association, to maintain complete secrecy, any operation that required opening the roof of HMB-1 was timed to avoid spying Soviet satellites overhead. Sea Shadow was delivered in March of 1985, followed by nighttime test voyages in 1985 and 1986 near the Santa Cruz Islands in Southern California. During the day, the vessel was safely secured inside HMB-1 for repair and maintenance. During trials, the crew saw huge wakes behind the ship that stood out on radar and from above, finding when they returned that the propellers were installed backward. Testing was suspended from 1986 to 1993 when the Sea Shadow was unveiled to the public, with testing concluding only a year later. Additional testing was done in 1999, and vessel operations were completed in 2006. The vessel was offered up for sale and even for donation to museums without interest, and in 2012 the vessel was sold along with HMB-1 with the requirement that Sea Shadow be dismantled for scrap.
Sea Shadow inside HMB-1. Visible is the retractable roof used for Glomar Explorer to load the claw and then retrieve the claw with the submarine from HMB-1 while it was submerged under Glomar Explorer. Image from Maritime National Park Association.
What about HMB-1?
Hughes Mining Barge 1 was originally built in 1973 to salvage the Soviet submarine K-129 from the ocean floor as part of Project Azorian, a subset of Project Jennifer. The Central Intelligence Agency (CIA) hoped to submerge HMB-1 under the Glomar Explorer and use a large claw device to capture the submarine and retrieve code books and other intelligence. The vessel acted more like a submarine than a barge, able to flood open ports at the bottom of its tanks and completely submerge, seen in the photos below. After performing a top secret submarine retrieval mission and becoming the Sea Shadow’s home for decades, it continues to live on as a dry dock for Bay Ship and Yacht in California.
“HMB-1 with the control barge Ore Quest visible on the left.” Image from Maritime National Park Association.
“HMB-1 fully submerged with the stability pontoons vertical during project Azorian.” Image from Maritime National Park Association.
Sea Shadow: an experimental vessel
The Sea Shadow wasn’t just built to test stealth technology – it also tested the SWATH hull, automation to reduce crew, rough weather seakeeping improvements, and radar and sonar control. The entire ship was wired with cameras to reduce the need for a large crew, and it had plenty of space for experiments. After construction, the vessel was also used to test advanced combat systems prototypes for passive identification and targeting, according to San Francisco Maritime National Park Association. Save for testing, the vessel never sailed for any other purpose, the sole function of Sea Shadow was to test technologies that were then applied to submarines and new Navy Destroyers. The vessel was so experimental that it didn’t even have a rudder and relied on stabilizers to steer, making the docking process even more impressive. The crew was especially note-worthy as the ship’s fuel tanks once took on water, and instead of a Navy tow, the crew spent 12 hours without power to restore one of the engines and make it home. Since the vessel was experimental, it didn’t have auxiliary power, so all the work was done in the dark with flashlights and the water removed from the ship by bucket brigade.
Sea Shadow entering a ballasted down HMB-1. Entry was tricky and relied on the pilot, no tugs were used and lines could not be thrown until Sea Shadow was inside HMB-1, causing missed lines and damage to the vessel at least once.
According to the Climate Online Redwood City, a crewmember said “We operated during the night with impunity…We could disappear and sneak up on whomever we wanted. Nobody thought we could do that.” The sailor also said in 12 foot waves, a glass of soda on the bridge barely rippled. More than once, Navy and Coast Guard escorts had to leave the vessel because of sea state 5 conditions with 8-12 foot waves, but the Sea Shadow was able to continue. It was described by the Navy as “the premier test platform for ship stealth and experimental technologies”, the ship that never officially sailed, but influenced technology for future naval vessels and was immortalized in games, models, and even movies like James Bond’s Tomorrow Never Dies.
An inside look at the Sea Shadow with a cutaway from H I Sutton.
We highly recommend checking out Maritime National Park Association’s article and photo tour of the Sea Shadow, they have some amazing photos and information!
Happy Fun Fact Friday!