If The Hunt for Red October taught us anything (besides the fact that Sean Connery makes for a horrible Russian) it's that submarines can be tracked by the sounds they make moving through the water. Well, not for much longer.
When a sub moves through the water, it faces two issues: One, the water it's displacing as it moves forward creates drag, which slows the sub down. Two, the wake it creates due to water rushing into the void left behind it is easily trackable. The Fluid Cloak, developed by Yaroslav Urzhumov and David Smith of Duke University, aims to solve both issues simultaneously.
The cloak is actually a mesh shell that surrounds the vessel, with different areas of the mesh being more permeable than others. In order to accomplish the actual cloaking, all water entering the mesh has to leave it at the same speed and direction as it entered. This means that while some spots would need to slow the flow of fluid, others would actually have to accelerate it as the sub passes—a feat accomplished by embedding millimeter-wide pumps, used for biomedical devices, throughout the mesh skin. We're still at least five years away from a working prototype, but when we're there? Finally an excuse for Crimson Tide 2. [New Scientist via The Atlantic]