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.