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Naval AD 20mm M71/08 weapon system with fire control system

Shipborne gun 20mm M71/08 is intended for close AD protection of small ships against attacks of the following aircraft: low-flying, low-speed craft and helicopters.   In addition to its main purpose, this weapon can be successfully used in day and night conditions against other sea, land and aerial targets, such as: small ships, patrol boats, different facilities on land, motor vehicles, troops, parachuters etc.

 

AA M71/08 WEAPON DESIGN FEATURES

The base of the gun 20mm M71/08 design are design solutions of 20mm M55 gun which has proven itself over many years of use as a highly reliable weapon in all conditions and a weapon easy to handle and maintain.

  • The main technical feature that M71/08 inherited, which represents a significant advantage over some other shipborne gun solutions of the same caliber, is the static balance of its elevating mass in all elevation angles even with the change of weight when the drum is emptied during firing. This static balance of the parts moving in elevation has the following advantages:
  • The gun can be elevated via the linkage (there is no need for separate equilibrators and gears) which makes the structure simple, the main parts and assemblies more reliable and reduces the maintenance costs at all levels;
  • By using adjustable shoulder rests and the sling, the gunner can track a target and lay the gun in traverse and elevation with great angular speed without changing body positions, which increases significantly the gun ergonomy ;

Shipborne 20mm M71/08 gun is shown in Figure 1.

 

AUTOMATIC 20MM M55 GUN

M71/08 weapon is fitted with an automatic 20mm M55 gun fed with ammunition from easily replaceable drums with the capacity of 60 rounds

Automatic 20mm M55 gun has been adapted to enable installation onboard ship:

  • The cannon and the ammunition feeding drum are turned (the drum is on the bottom side) and are protected with the cradle and case collector against water splashing (sea or river);
  • Hydraulic shock-absorber is adapted so as to enable smooth automatic operation of the gun
  • The gun is triggered by the right hand forefinger. The firing bar has a reliable effect at all elevation angles, and accidental triggering is prevented with a brake located on the weapon cradle.

The gun is fitted with a firing stop which profiles the action zone in accordance with the allowed action sectors (bearing in mind protection of the ship superstructure).

 

CARRIAGE AND OTHER WEAPON PARTS

The bottom support has the shape of a bell, and is designed so that the gun can be installed on different ship platforms without much difficulty and comparatively fast.

The seagoing fastener in elevation is at the gunner’s hand and it enables locking of the gun elevating mass at the angles of 0º, 30 º, 60º and 90 º.

The gunner can activate and release the seagoing fastener in traverse with his foot. There are 12 traverse positions (at every 30º).

 One crew member is sufficient to cock the gun, replace the empty drum or the case collector.

The gun has a water-proof casing which is fitted by putting the elevating mass at the elevation angle of 90º. The sighting devices have their own waterproof casing.

 

FIRE CONTROL SYSTEM

The Fire Control System (FCS) is a modular type system consisting of:

 

  • Day sights with a CCD camera for image display on PC monitor
  • Night sights with T.I. camera for image display on PC monitor,
  • Laser rangefineder,
  • Tablet PC, ballistic computer,
  • Day reflexive sights,
  • Boresighting telescope 20 mm.

 

CHARACTERISTICS OF CERTAIN FCS MODULES:

 

DAY SIGHT WITH CCD CAMERA
  •   optical zoom 36x
  •   field of view, horiz and vert.  46º - 4.6º

 

NIGHT THERMAL IMAGER

  •  Sensor type   Thermal imager uncooled  microbolometer sensor array
  •  Field of view :              10.4º x 8.3º
  •  Spectral band:             7.5 – 13.5 μm
  •  digital zoom  2x, 4x
  •  Operating Temperature Range:           -40°C to +80°C
  •  Target detection at object(4mx1.5m):              4,000 m

LASER RANGEFINDER

  •   measurement range                80 – 2500 m(5000 optional)
  •   wavelength, eye-safe             905 or 1.540 nm
  •   beam divergence      ≤ 1.5 mrad

 

DAY REFLEXIVE SIGHT

  • magnification             1 x
  • angle value of reticle radius 2.4º,  7.2º and 12º
  • field of view    horizontal 1800

                                   vertical       1800

BORESIGHTING TELESCOPE 20 MM
  • magnification              3,6 x
  •  field of view                5º

 

Use of the FCS in day and night conditons against various types of targets:

Measure the distance to target with the laser rangefinder, which positions the electronic reticle in the position that allows the exact elevation angle for shooting at the target. The image of the acquired target, the distance measured and the electronic reticle are displayed ono PC monitor. For the low speed targets and day conditions, the system is equpped with a reflexive collimator sight with illumination, which is especially suitable for shooting at airborne targets. This sight also serves as a backup in case of power failure.

The boresighting telescope is used to align the lines of sights with the gun barrel axis.

 

GUNNER’S PROTECTION

Gunner’s ballistic protection from the front is secured by the automatic gun and its cradle which are installed on the upper carriage, and he is protected from the side by an additional shield made of armoured steel plates connected to the upper carriage. This solution provides for gunner’s ballistic protection level IV (protection against small arms and infantry weapons, calibers 5.56mm to 12.7 mm);

WEAPON OPERATION

With the M71/08 shipborne weapon, the gunner follows the below stated procedure:

  • Adjusts the backrest to his height and fastens the rest with fasteners;
  • Adjusts the belt;
  • Leans with his shoulders against the backrest and puts the sling behind his back;
  • Grips the elevation handle with his right hand and releases the elevation seagoing fastener with his left hand;
  • Grips the left-hand elevation handle with his left hand and releases the traverse seagoing fastener with his right foot;

 

In day  and low visibility conditions, the gunner turns on the optoelectronic device and aims and tracks the target with the day camera or thermal imager camera.  The picture from the imager is transmitted, together with the projected recticle, to the tablet PC located at the gunner’s eye-level. So the philosophy of using the weapon in night conditions is very similar to the use of the reflexive sight in day conditions.

In backup mode the gunner assumes standing position with legs astride, partially leaning on the sling, and aims and tracks the target with the reflexive sight by putting his forhead at about 30mm from the rubber shock absorber of the sight. The gun is triggered with the right hand forefinger, while the other fingers hold the elevation handle. At dusk, the gunner can light the recticle by turning on the sight switch and adjust the light level on the potentiometer.

This upgrade concept of M71 gun has eliminated the need for the rotary contactor transmitting the signal from the bell to the upper carriage, because all the optoelectronic components are located on the gun parts moving either in traverse or elevation, which provides for a flexible use of M71/08 gun and opens wide possibilities for gun installation on different sea or riverine ships, patrol boats etc, all in accordance with the Buyer’s needs and requirements.