Lockheed Sea Shadow: when the U.S. made 50-meter catamarans “invisible”

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U.S. Navy Sea Shadow – San Francisco, Calif; March 1999

In the climate of tension and great secrecy of the early 1980s, in California the Lockheed Corp. was working to bring to life a unique object, an experimental design intended to study the naval applicability of the stealth technologies. Thus was born the
Sea Shadow
, a S.W.A.T.H. ship (a type of catamaran with fully submerged twin hulls) invisible to radar, although 49.99 meters long. It will never be framed in the armed forces, but the studies conducted will be revolutionary. The world will only know about her in 1994.

Lockheed Sea Shadow

Operational as a test and research ship from 1985 to 1986, the Sea Shadow was never officially commissioned, let alone operational among U.S. forces, and was decommissioned in 2012. Its purpose, after all, was anything but, which was to study “radar invisibility” technologies. A goal that proved successful, so much so that it was also recovered again in the late 1990s to base several fleet improvements on its studies, as well as the development of the DDG 1000 Zumwalt destroyers, from which the famous superyacht M/Y A was likely inspired.

Sea Shadow
Lockheed Sea Shadow – San Francisco, Calif.

Lockheed Sea Shadow – Development

The idea of developing the Sea Shadow was born in the late 1970s at Lockheed Corp‘s “Skunk Works” division, which is the team dedicated to developing the company’s experimental vehicles. Lockheed, then a major U.S. aerospace company, had completed the design and prototyping of its first stealth fighter (F-117) and considered declining the technology for naval applications.

The original idea involved the developments of stealth submarines but, rejected by the U.S. Navy, it was thus folded into the S.W.A.T.H. (Small WaterplaneArea Twin Hull), a specific type of catamaran where the cross section of the hulls on the sea surface is minimized, placing most of the displacement below the surface. Basically, a catamaran that, instead of having two displacement hulls, uses twin submarines instead of these-solution that, moreover, greatly improves overall stability.

Sea Shadow
Sea Shadow in shoal, note the SWATH configuration (Stephen Schafer – Wikimedia Commons)

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Lockheed Sea Shadow – Features

Undoubtedly singular, the Sea Shadow immediately jumps out at you because of the shapes of its volumes, angular and tilted at more than 45 degrees. In terms of size, it was 49.99 meters long and 20.73 meters high, with a draft of 4.42 meters. The reasons behind the shapes are, of course, stealth in nature, and thus designed to offer minimal reflectivity to radar. Feature that thus makes it virtually invisible detection and tracking systems. Legend has it that, in the middle of the night, she could get as close as the hatches of the ships with which she conducted her studies, undetected until her own hatches opened.

Lockheed Sea Shadow

As for the Swath configuration, the main platform is the nerve center of the ship, accommodation for 12 crewmen, command bridge, and navigation and research instrumentation. No armament is planned or present on board except for an emergency signal kit, with flares and smoke bombs. Below the surface, joined to the deck superstructure by two thin sloping surfaces, is the pair of twin keels. Siluroid in shape, each keel is equipped with a propeller and stabilizers, and because of the characteristics of this structure, it allows the vessel to maintain great navigational stability even in very rough waters, traveling at up to 12 to 14 knots. There are no rudders whatsoever, other than a hydraulic stabilization system, which is useful for both trim and maneuvering.

Sea Shadow – Command Bridge

Propulsion

In terms of propulsion, the Sea Shadow’s 536-plus tons were propelled by a pair of 750 KW Kato electric motors housed one per submerged keel. A solution adopted to limit submerged vibration as much as possible, thus also limiting submarine tracking. Powering the two electric motors were then two Detroit Diesel 12V 149 TI generators, this time installed and well isolated at the main deck. In a note released by Lockheed itself, an anecdote is told about the first sea trials, where, due to the high turbulence and wakes left in the stern, the team realized they had installed the propellers backwards.


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