science

Sonar decoy

Sonar decoy is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Sonar decoy rather than just read about it. In short: A sonar decoy is a device for decoying sonar. One may be released from a submarine or a surface vessel.

Key takeaways

Sonar decoy belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Sonar decoy to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Sonar decoy from memory before moving on to harder problems.

Reference excerpt

A sonar decoy is a device for decoying sonar. One may be released from a submarine or a surface vessel. A decoy acts as false targets for human operators or sonar-homing weapons such as acoustic torpedoes. Many count as a type of torpedo defence.

Submarine decoys

The first submarine decoys were the German Bold fitted to U-boats of World War II. These were a pellet of calcium hydride in a simple metal container. On contact with sea water, the calcium hydride decomposed to produce a trail of hydrogen gas bubbles that acted as a bubble curtain and reflected ASDIC impulses to produce a false target. The container trapped hydrogen and floated, with a crude spring valve to maintain buoyancy to keep it at a constant depth. Later decoys, such as Sieglinde, were motorised and could deploy their false target away from the host submarine, increasing safety.

Surface ship decoys Decoys were also used by surface ships to decoy the developing acoustic torpedoes. These were usually towed behind the host.

Example decoys

Bubble decoys Reflective bubble targets that produce an active return

Bold Sieglinde

Sonar jammers Siegmund - German "hammer and explosive decoy", intended to swamp the listening device with noise Acoustic Device Countermeasure (ADC) (US)

Signature decoys Foxer, a British towed decoy to decoy acoustic torpedoes away from surface ships. Also used by the US as FXR and the Canadians as CAT. Creates cavitation noises using water flow and metal banging noises (good-enough passive signature for the time). T-Mk 6 Fanfare. Towed, creates electrically-generated propeller noise (passive signature). AN/SLQ-25 Nixie - towed, active (since B variant) and passive Mobile submarine simulator - active and passive; swimming Maareech ATDS (India) Scutter (Israel) SCAD 102 (UK) MG-44 Korund-1 (Soviet) - swimming, active and passive; installed on Delta-class submarine (400 mm) MG-74 Korund-2 (Soviet) - swimming, active and passive; installed on Akula-class submarine (external "REPS-324 Shlagbaum" tubes) and Delta IV-class submarine (533 mm tubes) MG-104 Brosok, MG-114 Berill (Russia) - swimming, active and passive; installed on Akula-class submarine (external "REPS-324 Shlagbaum" tubes)

Combination Leonardo C30/S - combined jammer and moving signature decoy (Mobile Target Emulator) Ultra Electronics Next Generation Countermeasure - jammer, sensor, and signature decoy Ultra Electronics Surface Ship Torpedo Defence (SSTD) - sensor, jammer, decoy Ultra Electronics DCL Technology Demonstrator programme - sensor (passive AND active), hard-kill Rafael Torbuster - active/passive sonar decoy with hard-kill Vist-E (Russia) - jammer, active/passive decoy

References

External links

"Sonar decoys". uboataces.com.

Illustrations

Worked examples

Example 1 — a first encounter with Sonar decoy

Start with the simplest possible case. Write down what Sonar decoy claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Sonar decoy before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Sonar decoy ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Sonar decoy

In research: Sonar decoy appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Sonar decoy in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Sonar decoy is common in secondary-school and first-year university syllabi. It links to neighbouring topics German inventions, Sonar decoys, U-boats, so understanding it makes those chapters shorter.
In everyday life: Look for Sonar decoy outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Sonar decoy in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Sonar decoy means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Sonar decoy out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Sonar decoy in simple terms?

A sonar decoy is a device for decoying sonar. One may be released from a submarine or a surface vessel.

Why does Sonar decoy matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Sonar decoy?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Sonar decoy.