Introduction to Electronic Defense Systems
Second Edition

Filippo Neri

.

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Foreword
In my government position I am responsible for military research and technology for the Italian armed forces. During my coordination work with the
Western European Armament Group: Panel I1 (Research and Technology),
discussions have often been of a highly technical nature. It is certainly easier to make management decisions with an adequate technical background,
rather than having to grope with a poor knowledge of such technical issues.
As a result, I support any effort that has the objective of promoting an understanding of the many facets of military technology within the international
community of people in charge of armament matters.
Therefore, I greatly welcome Filippo Neri's easy and straightforward
explanations on the most recent developments in the electronic defense field,
from stealth technology to decoys, from electronic support measures (ESM)
to advanced jamming techniques. In particular, the principles underlying
low probability of intercept (LPI) threats, passive location techniques, the
benefits afforded by advanced digital receivers, towed decoy jammers, new
cross-eye jamming self-protection techniques, and high-power microwave
weapons, have been illustrated in very simple terms.
This book illustrates the significant progress that electronic defense
technology has made and is expected to achieve in the future with the advent
of advanced integrated systems (e.g., multifunction W systems and direct
energy weapons). The latter will not only represent effective aids to military
operations, but also act as a deterrent to any likely conflicts. Moreover, the

book describes how modern electronic defense systems operate and how they
can be put to use in the military operations of today and tomorrow.


xvi

Introduction to Electronic Defense Systems

Since this book has been revised and updated to account for the new
advances in electronic defense techniques and technologies, I am certain that
this second edition will be as popular as the first, which has been selected as
a basic EW textbook by many military colleges both in Europe and in the
United States. As an Italian officer, I must confess to be proud of it.
I hope that the insight gained from reading this book will help defense
personnel to better define their requirements and prompt the defense industries towards the development of high-performance, cost-effective, and
affordable systems.
Now that EW has proven to be a real deterrent and force-multiplier, I
hope that armed forces around the globe will realize the benefits that new
technological developments can afford and that these new assets will convince decision-makers to abstain from undertaking sad wars based on hardkill weapons and to pursue less destructive and more effective solutions
in order to arrive at no-casualty operations based on high-tech electronic
defense in support of political activities.

Major General Pietro Finocchio
Italian Air Force
August 2001


In my work as a designer of electronic defense equipment, I have often realized that there is no book, readily available to the designer, that explains the
principal functions of the different electronic warfare systems, what the vulnerable parts of radars are, what the limitations of weapon systems are, and
what makes an electronic defense system effective.

Taking advantage of my experience as a designer of radar and weapon
systems, I thought that a single volume describing the operating principles of
both weapon systems and electronic defense systems might be useful to those
wishing or needing to enter the field.
The book is addressed to those who are about to start working as
designers of these systems, to those who are or will become their users, and to
those who administer their procurement.
The formulas and the mathematical theory have been reduced to a
minimum, and readers are frequently invited to consult the appropriate references for in-depth analyses. The book can therefore be read and understood by anyone with a secondary education and interest in the systems used
by the armed forces.
The book is divided into eight chapters. Chapter 1 explains briefly the
usefulness of electronic defense, how it is organized, and what systems it
includes. In addition, it describes the operational objectives of electronic
defense.
Chapter 2 analyzes the sensors of weapon systems in order to highlight
their merits and, above all, their limits. The objective is to help the designer
exploit their weaknesses.
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Introduction to Electronic Defense Systems

Chapter 3 gives examples of ardlery and missile systems that use the
electronic sensors described in Chapter 2, again with the objective of emphasizing how their effectiveness may be reduced.
-chapter 4 describes and- analyzes electronic systems dedicated to
passive interception, generally known as electronic support measures (ESM).
Both those using radio-frequency emissions and those using infrared are
described.

Chapter 5 is devoted to the more striking part of electronic defense:
electronic countermeasures (ECM); that is, the generation of signals that, by
interfering with the receivers of "victim" systems, cause a degradation in the
performance of the associated weapon systems.
Since weapon systems can undergo intentional jamming aimed at
reducing their capabilities, they have been equipped with countercountermeasures (ECCM) systems. These systems and their applications are
described in Chapter 6, which gives an account of their effectiveness.
The thrust and parry of countermeasures and counter-countermeasures
seem to have no end,-and new technologies ensure that it is now possible to
attack the very operating principles ofweapon systems, which makes the
development of effective counter-countermeasures very difficult. Chapter 7
describes this technological
- advance.
Finally, to assist designers in achieving the optimum solution of the
design problems described in Chapters 4 and 5, Chapter 8 lists the criteria
that should be followed during the design stage of electronic defense systems.
Chapter 8 also discusses the methods of evaluation and simulation that can
determine whether a system is really effective. This should be particularly
helpful to those who have to decide on the choice of an electronic defense
system.
I hope that this book will be found useful. It is best seen as a simple reference book for the rapid evaluation and organization of material. In the end,
the quality of a system and the achievement of its operational objectives will
depend, as always, on the ability, the preparation, and the dedication of those
who have to perform the work.


Acknowledgments
I thank Enzo Benigni (president of Elettronica SpA), Gabriele Gambarara
(general manager), and Giuseppe Maresca (marketing & sales director), for
the encouragement they gave me while I was writing the second edition of

this book.
A special thank you to my first teacher on Radar Systems, Piero Guarguaglini (President of Finmeccanica) for the many discussions and suggestions
on Radar and EW techniques.
I also thank my colleagues at Elettronica SpA and at other firms and
organizations who have collaborated in the writing:
Andrea De Martino and V. Rossi for their help and for material on
radar systems; M. Grazzini for SAR technique; S. Scarfb and A. Zaccaron for
contributions to and revision of the material on digital receiver, DRFM, and
location techniques; S. Spillo for ESM receivers; F. Conte for ECM material revision; A. Bacchelli for advanced identification techniques; G. Pinto for
microwave technology; A. Zammit for electro-optics technology revision; G.
Broli and M. Stinco for ELINT systems; Candidoro Giannicchi for revision
of material on tracking systems; J. Marks for chaff revision; D. Autiero for
shared apertures; Michele Russo for contributions on telecommunications
systems; L. Girardi, G. Carlini, E. Nitoglia, and L. Caprioli for the artwork.
In particular, I thank: Ubaldo Menegotti, ESM & I W manager, Elettronica SPA, for information warfare; Vic Pheasant, international countermeasures director, Chemring Group Plc, for chaff and flares; and Silvano
Padovani, technical director, FIAR SPA, for airborne radar.

Filippo Neri
Rome, Italy
August 2001
xix


v

Contents
Foreword
Preface
Acknowledgments
1. Electronic Defense

1.1 Introduction
1.2 Systems in Use in the Armed Forces
1.2.1 The Air Force
1.2.2 The Navy
1.2.3 The Army
1.3 The Main Weapon Systems
1.4 The Objectives of Electronic Defense
1.4.1 The Organization of Electronic Defense
1.5 Electronic Defense Systems and Their Operational Objective
1.6 Information
1.6.1 Information Operation (IO)
1.6.2 Information Warfare (IW)
1.7 Need for the Study of Weapon Systems
References
2. Sensors
2.1 Introduction
2.2 Radar Sensors
2.2.1 Review of Electromagnetic Signal Transmission
2.2.2 The Radar Equation
2.2.3 Radar Equation in the Operational Environment
2.2.4 Radar Techniques
2.2.5 Search Radar
2.2.6 Synthetic Aperture Radar (SAR)
2.2.7 Tracking Radars
2.2.8 Airborne Radars (Interceptors)
2.3 Infrared Sensors
2.3.1 Review of Radiant Energy
2.3.2 Infrared Radiation Produced by Targets of Interest
2.3.3 IR Range Equation
2.3.4 Suppression of Background Effects

2.3.5 IR Systems
References
3. Weapon Systems
3.1 Introduction
3.2 Artillery Systems
3.2.1 Firing Accuracy
3.2.2 Susceptibility to Jamming of an Artillery System
3.3 Missile Systems
3.3.1 Command Missiles
3.3.2 Beam-Riding Missiles
3.3.3 Semiactive Homing Missiles
3.3.4 Active Homing Missiles
3.3.5 Track-Via-Missile (TVM) Systems

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3.3.6 Passive IR-Guided Missiles
3.3.7 Sea-Skimming Missiles
3.4 Passive Antiradiation Missiles
3.5 Laser Weapon Systems
3.5.1 The Laser
3.5.2 The Laser Equation
3.5.3 Laser Applications
3.6 Stealth Aircraft
3.7 Communications Systems
3.7.1 Networks
3.7.2 Types of Transmission (Links)
3.7.3 The Message
3.7.4 Examples of Communications Systems
3.8 Information Operations (10)
3.8.1 Information Cycle: The OODA Loop
3.8.2 Information Processes and Tools
3.8.3 Information Contents (on Subjects or Events)
3.8.4 Parameters Defining Information Value
3.8.5 Information in War Operations
References
4. Electronic Intercept Systems
4.1 Introduction
4.2 The Equation of a Passive System
4.3 Radar Warning Receivers

4.3.1 RWR Sensitivity
4.4 Electronic Support Measures
4.4.1 Omnidirectional Antennas
4.4.2 Antennas for Direction Finding
4.4.3 Frequency Measurement Receiver
4.4.4 Channelized Receivers
4.4.5 Direction of Arrival (DOA) Measurement
4.4.6 Pulsewidth Measurement
4.4.7 MOP Measurements
4.4.8 Automatic Detection
4.4.9 Identification and Data Processing
4.4.10 Presentation
4.4.11 Problem Areas in ESM
4.4.12 Typical Characteristics of a Naval ESM System
4.4.13 Range Advance Factor in the Operational Environment
4.5 Electronic Intelligence (ELINT) Systems
4.5.1 ELINT Sensors
4.5.2 Surveillance Network
4.5.3 The ELINT Processing Center (EWAC)
4.6 Advanced Passive Location Techniques
4.6.1 Doppler Shift
4.6.2 LBI
4.6.3 PRI Shift
4.7 Infrared Intercept Systems
4.7.1 Missile Launch Warner/Missile Approach Warner
4.7.2 Forward-Looking Infrared Systems

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4.8 Communications ESM and Communication Intelligence
4.8.1 Communications ESM
4.8.2 COMINT
References
5. Electronic Countermeasures Systems
5.1 Introduction
5.1.1 Operational Jamming Modes: SPJ, SOJ, and EJ
5.2 Onboard ECM Systems

5.2.1 Passive Systems
5.2.2 Active Systems
5.2.3 The Jammer Equations
5.2.4 The DRFM
5.2.5 Transmitters
5.2.6 ECM Antennas
5.2.7 The Pod
5.3 ECM Techniques
5.3.1 Spot Noise
5.3.2 Barrage Noise
5.3.3 Swept Noise/CW
5.3.4 Gated Noise
5.3.5 Amplitude-Modulated Noise/CW
5.3.6 Multiple False-Target Generation
5.3.7 Range Gate Pull-Off
5.3.8 Velocity Gate Pull-Off
5.3.9 Dual Mode
5.3.10 Inverse Gain
5.3.11 Countdown
5.3.12 Cooperative Jamming
5.3.13 Cross-Polarization
5.3.14 Cross-Eye (Virtual Off-Board Decoy)
5.3.15 Terrain Bounce
5.3.16 Illuminated Chaff
5.3.17 High-Resolution Radar Jamming
5.4 Infrared Countermeasures (IRCM)
5.4.1 Modulated Sources
5.4.2 Laser IRCM
5.5 Off-Board ECM Systems
5.5.1 Passive Systems

5.5.2 Active Systems
5.6 Communications Countermeasures (COM-ECM)
5.7 Information Warfare (IW)
5.7.1 Information Countermeasures (Counter Information)
5.7.2 Information Counter-Countermeasures
References
6. Electronic Counter-Countermeasures Systems
6.1 Introduction
6.2 Search Radar Counter-Countermeasures
6.2.1 Induced Counter-Countermeasures
6.2.2 Dedicated Counter-Countermeasures
6.3 Tracking Radar Counter-Countermeasures

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6.3.1 Induced Counter-Countermeasures
6.3.2 Dedicated Counter-Countermeasures
6.4 Infrared Counter-Countermeasures
6.5 Communications Counter-Countermeasures (COMECCM)
6.5.1 Frequency Hopping
6.5.2 Burst Transmission
6.5.3 Null Steering
6.5.4 Direct Sequence
6.5.5 Uniformity of Format
6.5.6 Encryption
References
7. New Electronic Defense Techniques and Technologies
7.1 Introduction
7.2 New Electronic Defense Architectures
7.2.1 ESM Antennas
7.2.2 Wideband Front End and Digital Receiver
7.2.3 Deinterleaving and Processing
7.2.4 Artificial Intelligence and Expert Systems
7.2.5 Display
7.2.6 Generation of Jamming Programs
7.3 ED Basic Technology Advances
7.3.1 MMIC Technology

7.3.2 Digital Processing
7.3.3 State of the Art in Infrared Sensors
7.4 Shared Apertures
7.4.1 Airborne Multifunction RF Systems
7.4.2 Naval Multifunction RF Systems
7.5 HPM Weapons (RFDEW)
7.5.1 Introduction
7.5.2 Electronic Systems Susceptibility
7.5.3 HPM Weapons
7.6 Anti-Antiradiation Missile Techniques
7.7 Antistealth Techniques
7.8 State of the Art and Perspectives
References
8. Design and Evaluation Criteria
8.1 Introduction
8.2 Design Criteria
8.2.1 Generalities
8.2.2 System Objective
8.2.3 Analysis of the Operational Environment
8.2.4 Possible Architectures
8.2.5 Verification by Simulation
8.2.6 Cost-Effectiveness Analysis
8.2.7 Risk Analysis
8.3 Evaluation Criteria for the Choice of a System
8.3.1 Generalities and Objectives
8.3.2 Definition of the Reference Operational Environment
8.3.3 Effectiveness of Electronic Defense
8.3.4 Cost-Effectiveness Ratio

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8.4 Operational Effectiveness
8.5 Electronic Defense and Conventional Defense
References
Glossary
About the Author
Index


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Electronic
1.1 Introduction
With the passing of time, electronic technology has come to play an increasingly important role in military operations. The electronic era, and with it
the first steps in the introduction of electronics.into weapons, goes back to
the time when radio and the radio direction finder were first used to give
the platform position. The second step was the introduction of radar for the
detection, and location in angle and in range, of hostile platforms, and its
subsequent use to increase the accuracy of artillery. The last step, and probably the most lethal one, has been the use of electronic devices for precision
guidance of missiles (Figure 1.1).
The effectiveness of electronically guided weapon systems, expressed in
terms of kill probability, has risen to values very close to unity, thus leaving
undefended targets little hope of escape. Consequently, almost all effective
weapons now employ electronic guidance devices. However, the sophistication of'today's weapon systems is such that they are rendered worthless
should their electronic circuits not operate correctly. As a result, it has
become essential to develop counter electronic systems capable of reducing
the effectiveness of weapon guidance devices.
The fruitfulness of these countermeasure techniques has quickly
become ,apparent. They have been developed to the point that they can
seriously degrade the performance of nearly all weapon systems (Figure 1.2).



2

Introduction to Electronic Defense Systems

Figure 1.1 A missile system exploits radar signals to hit its targets with precision.

Figure 1.2 The aim of an electronic defense system is to incapacitate the enemy's
weapon systems by generating electromagnetic jamming signals.


Electronic Defense

3

The inevitable next step has been the development of countercountermeasures to try to restore the original effectiveness of the weapon
sensors.
The techniques and technologies that lead to the construction of
devices capable of electronically countering a weapon system, and to the
development of counter-countermeasures, go under the name "electronic
warfare." However, given the basic harmlessness of these electronic systems-"electrons don't make holes," at least as long as no directed-energy
weapons are available-the
name "electronic defense" seems more
appropriate.

1.2 Systems in Use in the Armed Forces
In every country, the armed forces have at their disposal a number of weapon
systems, each with a different function. The following brief survey of the
missions of the navy, army, and air force will help to identify the main

weapon systems against which electronic defense must operate.
It should be emphasized that the aim of this survey is the identification
of electronically guided weapon systems, without reference to any specific
military organization. Moreover, systems pertaining specifically to nuclear
warfare are outside the scope of this book; only systems used with conventional armaments will be discussed.
Generally speaking, the mission of an air force is the surveillance and
defense of the sky above national territory; the mission of a navy is the surveillance of the seas surrounding national territory and protection of important sea routes; and the mission of an army is the protection of the national
territory itself.
1.2.1 The Air Force

An air force has to provide air defense of the national territory, coordinating
its own systems with those of the other armed forces. That is, the air force
must:
Contribute to the survival of important centers;
Inflict losses and give attrition when attacked by an enemy;
Ensure the neutralization of important military objectives in enemy
territory;


4

Introduction to Electronic Defense Systems

Give air support to land and sea action;
Ensure air transport;
Execute reconnaissance as necessary.
Under hostile air attack, survival of important centers and attrition of the
enemy are achieved by combining the use of a surveillance (or search) radar
network with the deployment of air forces in the area where an incursion has
been detected.

Such a combination is called an air defense network. Air defense search
radars are characterized by high sensitivity, and can detect and give early
warning of, the approach of targets at long ranges. They are sometimes called
early warning radars (EWR) and are characterized by high sophistication
and reliability, as they must operate continuously in the complete range of
environments.
Because of their sensitivity, they can give broad cover to the national air
space. The coordination of the data they provide and the correlation with
other information (data fusion) take place in special command and control
centers, where operational decisions are taken.
In time of peace, upon the detection of a suspect aircraft (i.e., one that
has not spontaneously revealed its identity), the search centers warn an air
unit, usually consisting of two very fast and maneuverable fighter aircraft,
and (with the help of an appropriate communications system) guide it
toward the position of the aircraft that has to be identified. The interceptor
fighters approach the target, identify it, and either let it pass or force it to
retrace its steps or to land (Figure 1.3).
In time of war, the procedure is different. As soon as the presence of an
alien aircraft has been discovered, the fighters (Figure 1.4) take to the air with
quite different intentions. They are still guided from the coordination center
and try to locate the target as soon as possible with their own onboard radar.
Identification is made with the help of identification of friend or foe (IFF)
equipment, devices for automatic recognition of friendly and hostile platforms. If the result warrants it, they lock onto the target and fire at it with
their onboard weapons (usually air-to-air missiles). They then try to make a
"kill assessment" to determine the amount of damage suffered by the target
and finally make their way back to base. If the target is not immediately hit
by a long- or medium-range missile, the fighters will have to approach closer
to the intruding aircraft, starting a series of dogfights either by launching
short-range missiles, usually infrared-guided, or by firing their onboard
cannon.



Figursl.3 The air defense network detects and locates all aircraft penetrating into
national air space.

Figun 1.4 The task of fighter aircraft is to ensure air space superiority. The photograph
showsthe European fighter aircraft (EFA).


Introduction to Electronic Defense Systems

6

Surveillanceof air space can be conducted directly by air patrols or by a
nerwork of air defense radars.
The neutralization of military objectives of special importance on
enemy territory is achieved by sending special strike aircraft (Figure 1.5) and
bombers. Strike aircraft make coven surprise attacks with a few units
approaching the target at very low altitude. Bomber tactics entail a powerful
attack by many aircraft, aided by fighters, with radar and electro-optic sensors being employed to locate and identify their ground targets.
In its air support role, the air force cooperates with ground forces
to stop the advance of enemy forces. It launches air raids against advancing
enemy columns and bombs their tanks and support services (the ground
attack function). This function is carried out by fighter-bombers (Figure 1.G).
which are extremely maneuverable aircraft fitted with a rariety of air-tosurface weapon systems.
In addition, the air force will usually have to provide for the defense of
its own bases, airfields, and services.
To sum up, in order to be able to carry out the Functions detailed
above, the air force will require the following systems:
SurveiILmcc andsearch ytm,consisting of land-based search radars


(Figure 1.7) positioned on high ground (i.e., mountains, high hills)
to offset the limitations of radar range at low altitude, as explained in
Chapter 2;
Airborne suwciIlancc and search ~ y s m
(Figure 1.8). These systems
are similar to the preceding ones but weigh less, and can therefore be

Figuml.5

Strike aircraft are entrusted with the task of hitting important military objee
tives on enemy ground. The photograph shows the Tornado in ks IDS version.


Figurs1.6 The high maneuverability of fighter-bombers allows for quick raids against

enemy ground forces. The photograph shows the ltalo-Brazilian AMX
fighter-bomber.

Figurn 1.7 The early detection and acquisition of targets is ensured by search radars.
The photograph shows the RAT 31s search radar for land-based installations.


Introduction to Electronic Defense Systems

8

Figurel.8

Airborne search radars permit detection of targets flying at low altitude. The

photograph shows the airborne warning and control system (AWACS).

carried on board aircraft having long-range capabilities without refueling. Such systems help to solve the problem of intercepting lowlevel targets at adequate ranges. A very detailed control of a territory
can be achieved by airborne side looking aperture (or antenna)
radars (SLAR) that exploit synthetic apermre radar (SAR) technique. These radars are able to provide detailed images of the controlled territory even at night or in presence of clouds;

Fighters, characterized by very high speed and maneuverability, fitted with:
1. Radar systems for target acquisition and cracking (airborne interceptors) (Figure 1.9). An onboard radar of this type is ser in the

front ofthe Fuselage and is protected with a tapering shell, which
is transparent to electromagnetic waves, called a radome (radar
dome);
2. Long-, medium-, and short-range air-to-air missile (AAM) systems (Figure 1.10);
3. Airborne weapon delivery systems for combat at very dose
range.

Sm'kc aircraj, for raids into hostile territory. These must be
equipped with (1) avionic radar for target acquisition and tracking;


Figum 1.9 Military aircraft exploit sophisticated radars for accurate target detection
and weapon guidance. The photograph shows the Grifo radar,

Figum 1.10 Sidewinder (IRI and Aspide (RFI air-to-air missiles installed on two F-104s.

(2) AAM a n d air-to-surface missile (ASM) systems; (3) b o m b control

and guidance systems (often this type o f aircraft is fitted w i t h



Introduction to Electronic Defense Svstems

10

terrain-following radar for blind navigation at very low altitude);
and (4) fighter-bombers for ground attack.
Besides all these, mention must be made of other aircraft assigned to the following missions:
Transportation;
Patrolling;
Training;
A surface-to-air missile (SAM)system, for the defense of airfields
and other objectives of vital importance. A missile system can be
long-range, for the defense of a zone or an area (area defense)
(Figure 1.1 I), or medium to short range for the defense of a site or
a point (point defense) (Figure 1.12). Usually, a missile defense
system consists of a local search radar (sometimes called acquisition

Figum 1.11

Long-range SAM systems are frequently employed to defend huge areas of
territory. The photograph shows the SAM Patriot system.



Introduction to Electronic Defense Systems

12

Convoy protection is carried out by well-armed naval vessels, which specialize in conflict with various potential attack systems such as submarines, aircraft, and other large ships. When some of a nation's interests lie Far From
its own territorial waters, it will be necwary to deploy aircraft carriers

(Figure 1.13) to ensure adequate air cover for the fleet. For the navy, too, the
system requirements will be on a par with those for air defense. In fact, what
is needed is the organization of the defense of the very wide area covered by
the whole fleet.
The following systems will therefore be required:
Shipborne and airborne EWR to prevent surprise attadc against such
a valuable target as a carrier;

Figure 1.13

Aircraft carriers give the necessary air cover to the fleet when it operates
tar tram national waters.


Electronic Ddmr

13

Fighters and strike aircraft, equipped with medium- and long-range
AAM and ASM systems.
Because of its enormous value, a carrier is usually escorted by other naval vessels such as cruisers, destroyers, and frigates. Ships of these three types conaitute the usual naval armament of those nations whose strong interests are
normally limited to their own territorial waters.
Cruisers (Figure 1.14) are heavily armed, medium to high tonnage
ships (8,000-20,000 tons displacement). They defend the formations
that they escort from air, surface, and underwater threats. Destroyers
(4,000-8,000 tons) are in practice large frigates equipped with a variety of
armament. Frigates (Figure 1.15) are well-armed, low- to medium-tonnage
ships (1,5004,500 tons) whose task is to provide an effective escort to other
ships in convoy or formation. Often they are designed for antisubmarine
warfare. Shipborne helicopters are frequently used in order to increase the

effectiveness of this role.
For patrolling not too far from coasts, moderately armed small tonnage
vessels are often used, including corvettes (200-800 tons) and sometimes
hydrofoils. Effective patrolling is often achieved with small- or medium-

Figure1.14

The Italian 'all-deck" cruiser Garibaldi allowing the usage of vertical and
shorttakeoff and landing (V-STOLI aircraft.