In today’s episode, we are going to discuss WHY ARE SUBMARINES SO HARD TO FIND?
Dubbed as the “Silent Service,” submarines are considered the most survivable weapons-delivery
platform. Submarine detection and monitoring was traditionally the exclusive domain of
highly classified military units specializing in naval anti-submarine warfare (ASW).
Military ASW employs technologies such as magnetic anomaly detectors
(MAD), which detect tiny disturbances to Earth’s magnetic field caused by metallic submarine hulls,
passive and active sonar sensors that use sound propagation to detect objects underwater,
as well as radar and high-resolution satellite imagery to detect surfaced submarines. Recent
advances in commercial tools and technologies now give open-source researchers some ability
to monitor submarine fleets. With commercial satellite imagery, synthetic aperture radar (SAR),
hydro-acoustic sensors, and even social media analysis, open-source researchers can better
understand the size and composition of countries’ submarine fleets, monitor the construction of
submarines and submarine bases, and potentially learn about patrol patterns and behaviors.
A submarine can be detected by a number of different sensors and methods.
Let’s check some of them: #1. Radar:
A modern submarine may from time to time pop up the periscope to verify its position
or visually ID a surface ship. It may have to also raise a radio mast to communicate via radio or
raise the radar mast to make a couple of radar sweeps. That's about all the submarine it's
going to expose above the surface. The radar cross-section of these masts is very small,
not much bigger than your forearm. The chance of detecting a periscope or mast with a radar
if there are any waves is very small, and the periscope is usually not up for very long
(the submarine often pops the periscope up, sweeps the horizon 360 degrees,
takes it down and analyzes the video recording of the sweep with the periscope down).
If the sea is calm and the periscope is up long enough, a radar can pick it up. A diesel-electric
submarine without AIP (Air Independent Propulsion) has to raise the snorkel to run the diesels and
charge the batteries, and this can definitely be detected by radar if the waves are not too high.
#2. Green laser: The green laser can give a very accurate picture
of the bottom of the sea in shallow waters, and also detect a submarine. However, the range is
very, very short and a helicopter or submarine basically has to fly right over the submarine,
and the sub can't be too deep. It is, so far, insignificant in terms of Anti-Submarine
Warfare (ASW). #3. Infrared:
Infrared emissions (in this case heat) can give away a submarine's position in typically three
ways: First way is heat emission from a snorkeling SSK or (ASW Submarine). While the second way,
the submarine's propeller stirs up water in its wake that eventually reaches the surface (if it's
not too far from the surface) that has a different temperature than the surface water. This creates
a "streak" behind the submarine of warmer or colder water that can be detected with FLIR
(Forward Looking InfraRed). And the third way is the periscope and masts may have a different heat
signature than the surrounding water and can be detected with infrared, but with the exception of
the snorkel, they are usually close in temperature to the ambient water and therefore hard to detect.
#4. Hydrodynamic Water Pressure: The submarine presses a lot of water
aside as it moves through the water. This causes a slight rise in the water level as it passes.
For obvious reasons, this is very hard to detect in the open ocean.
#5. Electronic Counter Measures (ECM):
This is lethal for a submarine. One sweep with the radar can not only give the bearing of the
submarine from the detecting surface ship away, but it can also tell the surface ship
exactly which type of submarine it is and even what range the submarine has set the radar to.
#6. Magnetic Anomaly Detection:
All submarines have some level of magnetic signature,
and this can be detected by an airplane or a helicopter if the submarine is near the aircraft's
position and near the surface of the sea. There are also fixed magnetic sensors on the seabed
near fixed naval mine stations and naval bases that can detect the magnetism from submarines.
#7. Passive sonar:
This is the main method to detect a submarine. It is essentially very advanced microphones
that listen to sound under the water. You don't necessarily have to be able to hear the submarine
with the naked ear, there are computers (such as LOFAR, LO Frequency Analysis and Ranging)
that can analyze the sound and find patterns that can tell a variety of information about the ship.
A nuclear-powered submarine has a nuclear power plant that has to be cooled by sea water
that is pumped around with a cooling pump. Even though the pump is made to be very silent, it
can be detected. An SSK running on battery power, and an SSK with Air Independent Propulsion (AIP),
basically doesn't get picked up on passive sonar unless it's going fast enough to cavitate. They
are quieter than the surrounding water. Surface ships can tow a passive sonar behind the ship
in a mile-long array. It can also deploy passive sonar buoys from its helicopter or from airplanes.
The primary advantage of passive sonar is that the target doesn't know it's been detected.
Finally, Active Sonar: Active sonar is like underwater radar,
except it transmits sound waves instead of radio. The difference is that sonar has far,
far less range than a radar since there is so much more reverberation in water than in air.
The primary advantage of active sonar is that you not only get a bearing
to the submarine but also the distance. However, the submarine can detect an active sonar at 2-5
times the sonar's detection range vs the submarine, so it can fairly easily move
out of the way when it hears the surface ship coming. For this reason, it is often useless
to zip around the ocean pinging away with your active sonar hoping a submarine will stay around
long enough for you to find it. Then, why with all these methods
of detecting a submarine are they so hard to detect? This is the core of your question.
In order to answer that, let's look at the submarine's and the ASW units pros and cons:
The submarine can hear (or detect with ECM) the ASW force on passive sonar long before
the ASW force's passive sonars can detect the submarine since the submarine is more silent.
An SSK with AIP (like the Swedish Gotland class) can basically not be heard at all.
As long as the sub doesn't transmit its radar or expose its periscope for too long,
it will always have to upper hand. In conclusion, An ASW task force is
flexible and can rely on the strengths of the different units to counter the
submarine's detection range advantage, but as long as the submarine is in a position where
it can allow itself to be very quiet, it will have the upper hand of knowing where you are
long before you know where it is, and then choose what to do with that advantage: lay low or attack.
Thanks for watching and see you in the next videos