Introduction
Stealth features have been incorporated into the design of submarines as the result of two trends. First, since Lockheed’s development of the F-117 Nighthawk stealth fighter, technology has been developed to reduce the radar cross-section of aircraft. The F-117 was the first specialized stealth platform. Today, it is rare for a new military airframe to be introduced that does not incorporate stealth features.
By definition, submarines were developed for stealth. By traveling submerged, they could sneak up on their adversaries without being seen. This resulted in the development of submarine detection technology – active and passive sonar. Passive sonar allows the antisubmarine platform to listen to sounds made by the submarine, differentiate them from other sounds in the environment, and render the sub vulnerable to attack. Active sonar sends out pulses of sound that bounce off the submarine, return to the antisubmarine platform, and reveal the sub’s position.
Since the 1960s, emphasis has been placed on passive sonar. This caused submarine designers to build ever more quiet subs. Today, submarines are so quiet, they are defeating detection by passive sonar. For example, the newest American Virginia class attack submarines are equipped with a silent magnetohydrodynamic drive, a form of “caterpillar” propulsion.
This has resulted in antisubmarine platforms reverting to active sonar detection. The pendulum has swung back to stealth. Submarine designers now have to design stealth features into their already quiet subs.
The F-117 Nighthawk and the Dawn of Stealth
In the 1960s, Pyotr Ufimtsev, a Russian electrical engineer and mathematical physicist, developed equations that predict the reflection of electromagnetic waves from two-dimensional and three-dimensional surfaces.
Ufimtsev’s work was published open-source. In the 1970s, Lockheed engineers seized on his equations and developed models to minimize the radar cross-section of objects. In simple terms, an airplane might have a wingspan of twenty feet. When struck by radar, it appears as an object with a wingspan of twenty feet. That is its radar cross-section. By applying Ufimtsev’s equations, Lockheed was able to minimize the radar cross-section of that airplane to something the size of a bumblebee. To that radar, it’s next to invisible.
Introduction
Stealth features have been incorporated into the design of submarines as the result of two trends. First, since Lockheed’s development of the F-117 Nighthawk stealth fighter, technology has been developed to reduce the radar cross-section of aircraft. The F-117 was the first specialized stealth platform. Today, it is rare for a new military airframe to be introduced that does not incorporate stealth features.
By definition, submarines were developed for stealth. By traveling submerged, they could sneak up on their adversaries without being seen. This resulted in the development of submarine detection technology – active and passive sonar. Passive sonar allows the antisubmarine platform to listen to sounds made by the submarine, differentiate them from other sounds in the environment, and render the sub vulnerable to attack. Active sonar sends out pulses of sound that bounce off the submarine, return to the antisubmarine platform, and reveal the sub’s position.
Since the 1960s, emphasis has been placed on passive sonar. This caused submarine designers to build ever more quiet subs. Today, submarines are so quiet, they are defeating detection by passive sonar. For example, the newest American Virginia class attack submarines are equipped with a silent magnetohydrodynamic drive, a form of “caterpillar” propulsion.
This has resulted in antisubmarine platforms reverting to active sonar detection. The pendulum has swung back to stealth. Submarine designers now have to design stealth features into their already quiet subs.
The F-117 Nighthawk and the Dawn of Stealth
In the 1960s, Pyotr Ufimtsev, a Russian electrical engineer and mathematical physicist, developed equations that predict the reflection of electromagnetic waves from two-dimensional and three-dimensional surfaces.
Ufimtsev’s work was published open-source. In the 1970s, Lockheed engineers seized on his equations and developed models to minimize the radar cross-section of objects. In simple terms, an airplane might have a wingspan of twenty feet. When struck by radar, it appears as an object with a wingspan of twenty feet. That is its radar cross-section. By applying Ufimtsev’s equations, Lockheed was able to minimize the radar cross-section of that airplane to something the size of a bumblebee. To that radar, it’s next to invisible.
The problem was that Lockheed had to arrange the slabs of metal that formed the airplane at specific angles in relation to each other to minimize that cross-section. The result was an airplane that was aerodynamically unstable and looked like a strange flying arrowhead. The F-117 Nighthawk is shown in Figure 1.
The F-117 became an effective strike aircraft, able to evade enemy radar and deliver bombs on target. But what does all this have to do with submarines?
Lockheed engineers made an accidental discovery. They tried to take pictures of the F-117 with Polaroid cameras and found that the camera could not focus.
The Polaroid autofocus system works with a sonar sensor. This shouldn’t be surprising. The discovery led to the design of stealth surface ships. Lockheed built a prototype stealth ship called the Sea Shadow (see Figure 2). Now, stealthy features are incorporated into most modern aircraft and surface combatants.
With the development of ultra-quiet submarines, antisubmarine platforms began relying less on passive sonar. They haven’t stopped using it, they just know it’s not as effective and has to be augmented by active search. Submarine designers have begun to incorporate stealth features into their hulls.
Diesel-electric submarines are very quiet. In a world where nuclear submarines are the superstars, these smaller “conventional” boats are often underestimated. They are cheaper than nuclear subs, and are becoming increasingly sophisticated and capable. They are particularly effective in shallower seas, littoral regions, and over shorter ranges. Germany, Norway and Sweden all built conventional diesel-electric submarines for use in the Baltic. Iran and other middle eastern countries also operate diesel-electrics.
The Germans and Norwegians collaborated on the Type 212 series of diesel-electric submarines. A number of these hulls were also built for the Italian Navy. These boats, in particular the German and Italian units, were built with bespoke features to assist in naval special operations. For example, in some units, an enlarged torpedo tube was incorporated to fit special operations equipment. In another, a piggyback hangar was designed to carry something like our SEAL Delivery Vehicle. Other models had side-mounted special operations pods.
The Italians wanted a larger boat to operate in the Mediterranean. The Germans thought that was a good idea. They collaborated with the Norwegians to develop the Type 212CD (“Common Design”). The CD was larger than other Type 212 variants. It was also longer. Of particular interest, it was designed with a stealthy hull to help it defeat active sonar. Look at its cross-section in Figure 3.
Compare the cross-section of the Type CD to that of the Type A. The Type CD is at the bottom right of Figure 3. It is immediately apparent that its hull has a faceted, diamond-shaped appearance. This design has been optimized to minimize the submarine’s “Target Echo Strength,” a measure of sonar effectiveness comparable to an aircraft’s radar cross-section.
Figure 4 shows a view of the Type 212CD from the starboard quarter. It illustrates the flat, slab-like facets of the hull.
This video summarizes the development of stealth subs and the Type 212CD:
Germany is not alone in incorporating stealth features into newer hulls. Both Russia and the United Kingdom have nuclear submarines with stealthier designs. The United States, with the caterpillar drive built into the newest Virginia class, has yet to incorporate stealth into its hull designs.
Of course, there are tradeoffs. The F-117 is not the most aerodynamic aircraft. A stealthy hull like that of the Type 212CD may give up in speed what it gains in stealth.
We can be sure of one thing. Work will continue in the fields of both stealth and detection. The major players cannot afford to fall behind.
About the Author
Cameron Curtis has spent thirty years on trade floors as a trader and risk manager. He was on the trade floor when Saddam’s tanks rolled into Kuwait, when the air wars opened over Baghdad and Belgrade, and when the financial crisis swallowed the world. Having written fiction as a child, he is the author of the Breed action thriller series, available on Amazon.
Check out his new Breed thriller, BLOOD SPORT, here:
The Type 212CD is featured in Book 6, White Spider. See all the books here:
Editor’s Note: Looking for a great Summer read? Check out the Breed series of thrillers. You can’t go wrong here. – GDM
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Disclaimer: SOFREP utilizes AI for image generation and article research. Occasionally, it’s like handing a chimpanzee the keys to your liquor cabinet. It’s not always perfect and if a mistake is made, we own up to it full stop. In a world where information comes at us in tidal waves, it is an important tool that helps us sift through the brass for live rounds.