Shkval, on the other hand, uses a rocket engine. That alone is enough to make it fast, but traveling through water creates major drag problems. The solution: get the water out of the path of the torpedo. But how, exactly does one get water of the path of an object in the middle of an ocean?

The solution: vaporize liquid water into a gas.

Shkval solves this problem by diverting hot rocket exhaust out of its nose, which turns the water in front of it into steam. As the torpedo moves forward, it continues vaporizing the water in front of it, creating a thin bubble of gas. Traveling through gas the torpedo encounters much less drag, allowing it to move at speeds of up 200 knots. This process is known as supercavitation.

The trick with maintaining supercavitation is keeping the torpedo enclosed in the gas bubble. This makes turning maneuvers tricky, as a change of heading will force a portion of the torpedo outside the bubble, causing sudden drag at 230 miles an hour. Early versions of Shkval apparently had a very primitive guidance system, and attacks would have been fairly straight torpedo runs. //

the gas bubble and the rocket engine are very noisy. Any submarine that launches a supercavitating torpedo will instantly give away its approximate position. //

Another drawback to a supercavitating torpedo is the inability to use traditional guidance systems. The gas bubble and rocket engine produce enough noise to deafen the torpedo’s built-in active and passive sonar guidance systems. Early versions of the Shkval were apparently unguided, trading guidance for speed. A newer version of the torpedo employs a compromise method, using supercavitation to sprint to the target area, then slowing down to search for its target..