M551 Sheridan

M551 Sheridan
M551 Sheridan in Vietnam, 1969
General properties
crew	4 (commander, driver, gunner, loader)
length	6.3 m
width	2.8 m
height	2.3 m
Dimensions	15.2 tons
Armor and armament
Main armament	1 × 152 mm cannon with 20 HEAT-T-MP shells and 8 Shillelagh guided missiles
Secondary armament	1 × 7.62 mm M240 - machine gun (paraxial) 1 × 12.7mm M2HB machine gun
agility
drive	Detroit Diesel 6V-53T, water-cooled 2-stroke V-6 diesel engine 220 kW (300 PS )
suspension	Torsion bar
Top speed	69 km / h (road)
Power / weight	14.5 kW / t (19.7 hp / t)
Range	560 km

The M551 Sheridan was a light armored time of the Cold War from American production, named after Civil War General Philip Sheridan . It was developed in the early 1960s when it was discovered that the arsenal of the US armed forces was missing an airborne reconnaissance tank.

development

In 1958 the predecessor project of the Sheridan, the reconnaissance tank T92, was discontinued due to the lack of amphibious capabilities of the prototypes. The following year, under the acronym was ARAAV ( A rmored R econnaissance A irborne A ssault V ehicle) developed a new concept for a tank, which should both have the qualities of a reconnaissance tank, as well as an airborne tank. In doing so, emphasis was placed on amphibious properties, the possibility of parachute dropping and strong armament. A total of twelve proposals from various companies were submitted, with the Cadillac Motors Car Division model being selected for further development. The centerpiece of the vehicle was the XM81 Shillelagh Combat Vehicle Weapon System . The Kennedy administration, with Secretary of Defense Robert McNamara, accelerated the program as more emphasis was placed on conventional armed forces and McNamara preferred technical solutions to tactical problems. However, since the first attempts with the Shillelagh system in the fall of 1961 were disappointing, various other types of armament were considered for the Sheridan. This included conventional armament with a drawbar cannon, a drawbar cannon in combination with the French ENTAC system or pure guided missile armament with the TOW or Polecat system. Since the two missile systems were also not yet operational, the choice fell on a 152-mm drawbar cannon, which could fire conventional ammunition in addition to the Shillelagh missiles, so that the armament could have been retained if the guided missile tests were stopped. However, further testing of the Shillelagh was satisfactory.

An M551 with attachments to represent a T-80

Since the 152 mm combination weapon was a novelty, a lot of emphasis was placed on testing the turret with the weapon in the subsequent development. In August 1962 a prototype of the turret was mounted on the hull of an M41 to test the weapon with the conventional ammunition. Prototypes of the hull and chassis were subjected to tests from June 1962. During the tests, the prototypes underwent a total of four major changes, the design of the fifth prototype was adopted for production.

The budget for the production of the M551 Sheridan was approved on April 12, 1965. In May 1966, the design of the last prototype was established as a master sample, although serious technical defects were still present in March. The reason for this was the US Army's concern that funding for further tests could be suspended, which would have meant the end of the entire project. The shortcomings related to safety, durability, reliability, performance and maintenance. The Army's Test and Evaluation Command (TECOM) designated the M551 as unsuitable for use. Nevertheless, series production began in 1966. 1662 vehicles were produced up to November 1970. The total cost amounted to about 1.3 billion  US dollars , representing a cost overrun of 80% compared to the originally estimated cost.

In 1989 the Sheridan was subjected to a combat upgrade. The unreliable smoke device was replaced and an AN / VSG-2 thermal viewing device was installed, which gave the Sheridan night combat capability. The driver could use a residual light amplifier. The new name was M551A1 (TTS). A total of 70 vehicles were to be converted, however, with the outbreak of the Second Gulf War , only 60 vehicles could be converted before they were flown to Saudi Arabia .

The Sheridan was only used by the US Army, only a single copy was tested by Australia, but rejected as unusable.

Today, a few copies of the Sheridan are still used to represent enemy targets in combat training centers. Vehicles of Soviet origin such as the T-80 , BMP-1 or the ZSU-23-4 are to be represented by conversions and additions .

technology

Armament and ammunition

An M551 shooting down a Shillelagh

The main armament of the Sheridan is the 152 mm M81 cannon. This is able to fire both conventional HEAT-T-MP ( H igh E xplosive A nti T ank - T racer - M ulti P urpose, shaped charge - multi-purpose projectile with tracer ) ammunition with a combustible case and the infrared-guided Shillelag guided missile . With the stationing in Vietnam, the M625 Canister projectile was also developed, which is filled with around 10,000 flechets and is used to combat infantry. The elevation range of the weapon system is −8 ° to + 19.5 °, the lateral range is 360 °. The straightening is done by an electric drive, the pivoting of the tower through 360 ° takes ten seconds. The ammunition for the main weapon is stored on the left side of the turret and under the weapon system as well as in the tub next to the driver. The combat load consists of 20 HEAT cartridges and eight guided missiles.

The secondary armament consists of a Browning M2 machine gun with 1000 cartridges on a mount on the commander's hatch and a coaxial machine gun in caliber 7.62 × 51 mm NATO with 3000 cartridges.

An M176 smoke throwing system is available to the vehicle for fogging. Four pipes are attached to each side of the tower.

The weapon system gave the Sheridan considerable firepower, but at the same time proved to be very problematic. The combustible case of conventional ammunition was very sensitive to moisture and damage. If the humidity was too high, the case swelled up and could no longer be inserted into the cartridge chamber; if handled too roughly, it could tear open and distribute the highly combustible propellant powder in the tank. After a cartridge was fired, glowing powder residues were often left in the chamber, which could ignite the next cartridge when it was inserted. To solve this problem, a compressed air system (Open Breech Scavenging System - OBSS) was installed to blow the glowing residue out of the pipe. However, it turned out that the remains were blown into the fighting compartment, where they could ignite the ammunition that was still in storage. The system was then modified so that when the shutter was still closed, it blew out the remains (Closed Breech Scavenging System - CBSS) . The firing of the cannon also produced an extremely high recoil, which could not be compensated by the low weight of the vehicle, so that the first two rollers sometimes lifted off the ground when fired. This strong recoil also disrupted the electronics of the missile's steering system, so that it often signaled not ready after a grenade had been fired . The guided missiles theoretically gave the Sheridan the ability to destroy battle tanks, but these too were defective. Since the Shillelaghs were infrared controlled, the control did not work if the sun was at an angle of ± 20 ° to the longitudinal axis behind the tank.

Armor

The Sheridan's tub is made of welded aluminum , alloy 7039, which has a positive effect on the overall weight and buoyancy, but only offers moderate protection. The tower is made of armored steel for better protection of the crew. In Vietnam it turned out that the armor did not offer sufficient protection against fire from RPGs . In the event of a hit in the unprotected ammunition magazine or the tank, the vehicle often caught fire. If this could not be extinguished, the high temperatures caused the aluminum to lose its load-bearing effect and the entire tub collapsed. The tower remained externally undamaged in such a fire, but was unusable.

Drive and drive

The Sheridan is powered by a water-cooled six-cylinder 2- stroke diesel engine with turbocharging . The unit develops an output of 220 kilowatts (300 hp). The engine is located in the rear of the vehicle. The high performance of the engine in connection with the low weight gave the vehicle a mobility that was unique up to then.

The drive consists of five rollers, each with a pulley at the bow and the drive wheels at the stern. The suspension is provided by torsion bars, and shock absorbers are also attached to the first and last rollers.

Swimming and air landing ability

An M551 when released using LAPES

The low weight of the Sheridan made the vehicle more buoyant, but preparatory measures were required to cross water. To do this, a flotation collar that was integrated into the tub had to be extended to give the vehicle more buoyancy. The drive in the water was via the chains and accelerated the vehicle to a maximum of 6 km / h.

For use as an airborne tank, there were three different methods of bringing it to the scene. For normal air transport, the vehicle could be transported in full combat equipment in the C-130 Hercules and the C-141 Starlifter and used immediately (full roll-on roll-off capability). For combat use, the tank was either dropped on a shock-absorbing pallet with eight parachutes (Low Velocity Air Drop - LVAD) or dropped from a height of about three meters with a braking parachute. For this purpose, the aircraft flew at the lowest speed (around 150 km / h) and minimum altitude with the tailgate open over the drop zone. The Sheridan was stored on a shock-absorbing pallet, was pulled out of the aircraft by small parachutes and was then supposed to be slowed down by a large parachute. After the impact, however, the tank slid a few hundred meters beyond the landing zone due to the high dropping speed. Several Sheridans were completely destroyed in this type of drop. The procedure was as Lapės ( L ow A ltitude P arachute E Xtraction S denotes ystem).

crew

The crew of the Sheridan consists of four soldiers, the driver, the commander, the gunner and the loader. The driver sits in the front center of the tub. The commander has his place on the right side of the tower, the gunner sits in front of him. The loader sits on the left side of the turret. Due to the small size of the vehicle, the crew has very little interior space available. In hot areas such as Vietnam, the limited space combined with the high temperatures led to rapid fatigue of the crew, which affected the rate of fire. In Vietnam, the tower crew often drove on the tower roof due to the high threat posed by mines. In addition, hits in the ammunition magazine caused a destructive fire or explosions inside the vehicle.

Technical specifications

designation	M551 Sheridan
Type:	Reconnaissance and airborne tanks
Crew:	4th
Engine:	General Motors 6V53T six cylinder 2-stroke diesel engine with turbocharging
Power:	300 hp at 2800 rpm
Transmission:	Allison XTG-250-1A with four forward and two reverse gears
Landing gear:	torsion bar sprung roller drive
Length over all:	6307 mm
Width over everything:	2800 mm
Height above everything:	1900 mm
Ground clearance:	480 mm
Wading ability :	amphibious
Trench crossing ability:	2400 mm
Climbing ability:	840 mm
Gradeability :	60%
Bank slope:	40%
Combat weight:	15,120 kg
Maximum speed road:	69 km / h
Top speed terrain:	36 km / h
Fuel quantity:	598 liters
Driving range:	560 km
Armament:	152 mm M81 combination weapon, 1 Browning M2 heavy machine gun , 1 7.62 mm machine gun of various types
Ammunition:	20 projectiles for the gun, 8 guided missiles, 1000 cartridges for the M2, 3000 cartridges for the 7.62 mm MG

Mission profile

The Sheridan should be able to perform several tasks. Due to its small size, low weight, buoyancy and high mobility, it should be suitable for combat and reconnaissance. In airborne operations, he should support the infantry with his firepower and provide the airborne troops with anti-tank capabilities. At the same time, it should be an inexpensive but effective weapon to defend against large tank formations in the event of an attack by the Warsaw Pact on NATO territory .

Calls

An M551 during maintenance work in Vietnam

An M551 with ammunition during Operation Desert Shield, 1990

The Sheridan was first used in Vietnam, although its primary task was actually anti-tank defense and conventional tank battles did not take place in Vietnam. The stationing took place mainly on the advice of General Creighton Abrams, who wanted to assign the Sheridans, who had been stored in the depots, to a task. A commission of experts was convened to evaluate the Sheridan with regard to its suitability for use in Vietnam, but came to the conclusion that the vehicle in its current configuration would have only very limited use. As a result, only 64 Sheridan were sent to Vietnam. In these vehicles, the fire control system for the Shillelagh was removed and the hull armor reinforced with titanium in order to counter the high threat posed by mines. Guided missiles were not carried. To protect the commander, ballistic protection was attached to the mount of the M2.

The troops in Vietnam were initially not very happy about the equipment with another lightly armored vehicle. After the first skirmishes with the use of M625 ammunition, however, it turned out that the Sheridan offered good support for the M113 , which were only armed with machine guns . At the same time, it had better cross-country mobility than the heavy M48 . Because of this, another 200 vehicles were brought to Vietnam by 1970. A total of around 300 Sheridan were damaged by RPGs and mines during their deployment in Vietnam, some of them several times. 90 vehicles were total losses.

In 1989 ten Sheridans were deployed as part of Operation Just Cause to support the paratroopers of the 82nd Airborne Division against the lightly armored vehicles of the Panamanian armed forces. The so far only parachute drop from tanks was carried out in combat. During the advance, the Sheridans used their guns against road blockades.

During Operation Desert Shield 1990/1991, the M551s were among the first armored vehicles to arrive in Saudi Arabia, forming a first line of defense against the Iraqi forces. During Operation Desert Storm, the 82nd Airborne Division was used as a flanking force. During the forays through the desert, the Sheridan was used for the first time against battle tanks, the Shillelagh guided missiles were fired for the first and only time in battle. Several T-55 tanks were destroyed by the Sheridans.

literature

• Steven Zaloga : M551 Sheridan - US Airmobile Tanks 1941-2001 , Osprey Publishing, ISBN 978-1-84603-391-9

Web links

Commons : M551 Sheridan  - Collection of images, videos and audio files