A faint trace appears on the starboard side of the screen, indicating something far away is making noise in the water. The young broadband operator listens and classifies it as biologics—just like the other hundreds of traces he has seen on this watch. It soon fades out—just like the other traces. There are a few contacts on the port side, merchant ships that have been tracked since the beginning of the watch. The watch team is searching for the new Chinese submarine. Intelligence says it left port under the cover of night heading east. Another thin trace on the starboard side, but as the broadband operator scrolls over to interrogate, a ping draws everyone’s attention back to port.
The fatigue of deployment is forgotten with the sharp sound of an active sonar ping. It is on. Broadband scrolls his cursor over to the active and calls out the bearing to the sonar supervisor. The captain arrives as battle stations is called away. “Narrowband, find that submarine!” he calls out. Another ping echoes through the hull. A trace down the bearing of the active begins to draw forward as the unknown contact closes.
A shooting solution is obtained, a torpedo is launched, and they watch as the weapon collides with the contact. Before they have time to catch their breath a sharp sound erupts on the screen on the starboard side as a new trace draws forward. The trace that was thought to be biologics was actually their target, and their location was revealed when they fired at the drone. “Torpedo in the water!” The ship launches countermeasures and takes evasive maneuvers. An explosion shakes the submarine as the weapon hits the countermeasures.
After reviewing the time history, there was no acoustic information to indicate there was a submarine, even with the newest arrays. The Chinese boat was equipped with the newest sound silencing technology; the only way to detect it was by a transient (or unintentional) noise, which might be unrecognized or missed. The active contact originally received was a Chinese drone sent to find and send ranging information using active sonar to the Chinese submarine. The U.S. boat’s location was revealed before it had even fired at the drone, despite remaining acoustically undetected until pinged by the drone.
This example, while fictional, could be possible in the future. Adversary technology and application are improving at a rapid rate. U.S. submarines will require new methods for detecting adversary submarines, which are likely to continue to grow quieter and eventually could be undetectable through passive detection. In addition, submariners are perfecting the use of the marine environment to mask their acoustic propagation and remain undetected.
Luckily as technology improves, new frontiers open. Drones, unmanned underwater vehicles, and unmanned aerial vehicles are presenting new options on the battle front—and potentially a solution to the problem of stealth. Drones can take risks U.S. manned forces cannot afford to take, such as using active sonar.
Passive sonar listens for noise in the water and can determine range based on the decibels. Active sonar sends out sound waves to find contacts that passive sonar does not pick up, either because they are dead in the water or transiting silently. The contact’ range is determined by analyzing the time it takes for the waves to return after they are transmitted.
Submarines use active sonar at periscope depth to find stationary contacts or to navigate under polar ice in the Arctic regions. However, active sonar has a major drawback. Sending out sound waves alerts enemies to a submarine’s location, instantly letting them know who and where it is. If there is a contact within range to detect the active, tactical security is lost.
However, if drones could use active sonar, a submarine could remain undetected while still having the benefits of going active. Drones would offer a tactical advantage, no matter how silent the adversary, by detecting contacts that could not be picked up passively and providing another form of ranging information. U.S. submarines could go on the offensive, actively searching for adversary submarines instead of relying on the enemy to make a mistake in the design or operation of their submarines.
A potential risk arises when it is time to take out the target. If the drone were unable to fire on the target for some reason, the submarine would need to fire its weapons, alerting the enemy to its location. The risk lies with the range at which the drone could operate and send data. If the operational range of the drone were known, it would reveal how far away the submarine was operating. Not only would the active sonar alert the enemy to the presence of the submarine, but it also would narrow down its location.
However, with technological advances, active sonar may become the best way to detect a cutting-edge submarine. A single drone could find and perhaps one day even classify a contact and strike—all without revealing its mothership’s location. While drones will not replace submarines anytime soon, their ability to use active sonar to detect an adversary could provide a tactical advantage. Eventually, multiple drones might operate in a wolfpack to hunt contacts, mitigating risk to force and mission and changing the game for the Silent Service.