May 7, 1979 marked a milestone in the history of the United States armored forces when the acquisition of the first 110 M-1 Abrams tanks was approved. This tank owes its name to General Creighton W. Abrams, Army Chief of Staff and commander of the 37th Armored Battalion, who led the armored assault that broke the German siege of Bastogne, during the Ardennes Offensive in December 1944. It can be said that the M-1 Abrams was the first newly designed American tank since the M-26 Pershing entered service in 1944. Since then, all US Army medium and main battle tanks had been evolutions of previous models.After approval for service of the new M-1 Abrams MBT, production began, with most of the components being built at the Lima Army Tank Plant in Ohio and assembly being carried out at the Detroit Arsenal Tank Plant. Production began at rate of 30 tanks per month during 1980 and 1981, 60 tanks per month during 1982 and 1983, and 70 tanks per month during January 1984, reaching a total of 2,374 M-1 Abrams manufactured until February 1984. The production M-1 tank had some differences with the XM-1 prototypes such as a modified turret roof extended rearward, the relocation of the crosswind sensor, installation of twin headlights instead of single ones and the change of the crew mounting step, from one angle iron to one flexible cable.The M-1 Abrams tank was a very complex and advanced vehicle in which many companies participated as subcontractors. For example, Cadillac Gage was responsible for the drive, stabilization and command system of the turret, Computing Devices Canada for the ballistic computers, Hughes Aircraft Company for the laser rangefinder, Kolmorgen Corporation for the gunner’s auxiliary sight, and Singer-Kearfott Division for the data link, among many others.The internal layout of the M-1 Abrams tank was conventional, with the driver at the front, combat chamber in the center and the engine group in the rear of the vehicle. The crew was made up of 4 people, driver, commander, gunner and loader. The driver was sitting in the middle of the hull in front in a reclining position because of the hull’s sleep slope. The rest of the crew were located inside the turret, with the commander and gunner on the right and the loader on the left.The driver had his own hatch and has 3 observation scopes, one of which can be exchanged for a night vision device. The steering control was very similar to a “T” shaped motorcycle handlebar, with rotating throttle grips. It was known among tankers as “Cadillac” because of its manufacturer, Cadillac Gage. The commander had 6 observation scopes and one aiming scope for the 12.7mm machine gun. He also had a sight for the gun that was associated with the gunner’s aiming system. Finally, the gunner (on the image) used a double magnification day/night main aiming system, a laser rangefinder and an elevation stabilization system. In addition, the commander, gunner and driver had night vision equipment.The power plant consisted of an Avco Lycoming AGT-1500C multi-fuel turbine engine that burns diesel, aviation fuel (JP-4 or JP-8) and gasoline. The driver only had to adjust a selector on a control panel to change the type of fuel to use. This engine developed 1,500 hp and gives the M-1 Abrams a high power-to-weight ratio of 27 hp/tonne, allowing it to accelerate from 0 to 32 km/h in just 6 seconds. The maximum speed is 72 km/h on roads and 48 km/h off-road, although it was stated that the tank was capable of reaching almost 100 km/h on road with the engine governor removed. Normally it was not allowed to travel at such speed to avoid damaging the tracks and to avoid the risk of serious accidents to the crew.The engine was mechanically simple and designed to make maintenance and repair tasks simple. It was estimated that the time between overhauls is about 20,000 km or about 1,800 hours, much longer than previous diesel engines. It was also a very quiet engine but emitted a lot of heat, which gave it a very high IR signature, and had a very high fuel consumption of about 390 liters every 100 km. Due to its ability to move quietly and perform fast attacks, the Canadians nicknamed them “whispering death” since the NATO Reforger’82 exercise. It had an Allison X-1100-3A Hydro-Kinetic automatic transmission with four forward and two reverse gears. The engine-transmission assembly has been designed to be changed in less than an hour.The running gear consisted of 7 double road wheels with three return rollers on each side of the hull. The suspension was entrusted to a system of torsion bars installed on each of the road wheels, with torsion dampers on wheels 1, 2 and 7. The drive sprocket was at the rear and the idler wheel was at the front and had a hydraulic control to adjust the tension of the track. This last element was installed so that the crew could easily tighten the track, since it had shown itself prone to coming off.The front hull and turret of the M-1 Abrams were built with armor similar to the British Chobham type, composed of several layers of steel, plastic, ceramic and kevlar. This material was not as ductile as steel and did not allow it to be molded into rounded shapes, hence the angular shape of the tank. These vehicles did not have spall liners although several 105mm rounds carried in the turret basket had covers made with material of this type. It was believed that the frontal armor offered the same protection as 700mm of rolled homogeneous armor (RHA) against HEAT rounds or 470mm of RHA against APFSDS rounds, although these data were estimates, since the specific data on the armor was top secret information.The survival of the tank was carefully studied and the vehicle carried some systems focused on saving the crew in case they were hit by the enemy. The crew compartment was separated from the fuel tanks and ammunition storage by armored bulkheads and a Halon automatic fire extinguisher system reacts within 250 milliseconds to put out any fire. In addition, there were several hand-held fire extinguishers distributed throughout the interior of the turret and there was another fire extinguisher system in the engine compartment that was activated from the left side of the hull.The ammunition ready for use was stored in armored spaces at the rear of the turret and was separated from the crew by a sliding armored door which closes automatically after the extraction of a round. In addition, this magazine had 3 top blowout panels that would explode upwards if hit, diverting the force of the explosion away from the interior of the turret. These first M-1 Abrams lacked NBC protective equipment, so in combat, the crew members carried NBC suits and masks on board for protection. However, the vehicle had an AN/VDR-1 radiological detection and alert system (RADIAC).The main weapon was a 105mm M-68E1 gun, that was an American version of the British L7 gun, built under license in the United States. This gun was the same carried by the M-60 MBT but with the vertical sliding breech block and other components used in the T-254E2 prototype gun. To improve the effectiveness of this gun, new ammunition was created, so this weapon fired HEAT, HEP, HE, APFSDS, white phosphorus, anti-personnel (multiple flechette) and instruction projectiles. Among the APFSDS ammunition (on the image) were the M-735A1 and M-774 rounds composed of depleted uranium or “staballoy” with greater penetration power than normal ones. This gun could fire between -10 and +20º elevation and the turret made a complete rotation in 9 seconds.The 105mm M-68E1 gun was chosen instead of the German 120mm because more ammunition could be carried in the vehicle and because at that time the German gun had various defects and was unreliable, although it was clear that this caliber would be the one installed in the future Western tanks due to their power and precision. However, the M-68E1 was still a very powerful gun with a lethality against tanks contemporary to the M-1 Abrams of about 3,000 meters.As secondary armament it had two 7.62mm M-240 machine guns, one coaxial with the gun and another mounted on top of the loader’s station, and a 12.7mm M-2HB installed on the commander’s station. It also carried two sextuple M-250 smoke grenade dischargers mounted one on either side of the turret front. The vehicle carried 55 rounds of 105mm, 1,000 rounds of 12.7mm and 11,400 rounds of 7.62mm.M-1 Abrams MBT carried a modern fire control system equipped with a Hughes laser range finder, a thermal sensor, a stabilized day/night thermal sight for the commander and the gunner and a Computing Devices Canada digital solid state ballistic computer. The thermal sight had two positions, “white hot” or “black hot” to obtain a clearer image of the target depending on the environmental conditions.Before shooting, the gunner placed the sights on the target, pressed the distance button and the laser rangefinder determined it. Then, the ballistic computer made the necessary corrections by evaluating other data such as external temperature, wind speed and the inclination of the tank. Additionally, the gunner can manually enter data into the system regarding ammunition type, gun wear, barometric pressure and ammunition temperature. Once the computer had all this data, it calculated the shooting coordinates and arranged the sight accordingly to fire.The first two M-1 Abrams were delivered to the US Army on February 28, 1980 in a ceremony held at the Lima Army Tank Plant, Ohio. The first tank delivered was baptized “Thunderbolt”, in honor of the one manned by the then Lieutenant Colonel Abrams in January 1945 when he rescued the 101st Airborne Division, surrounded by the Germans in Bastogne. These two tanks were delivered to Squadron H of the 2nd Batallion of the 6th Cavalry Regiment based at Fort Knox, Kentucky.In September 1980, Phase III testing began at the Fort Knox and Fort Hood bases, located in Kentucky and Texas respectively. The tests carried out at Fort Knox were carried out by four M-1 Abrams and were intended to collect data on reliability in a field environment and on the maintenance, availability and durability of the running gear. These tests continued until May 1981, and in them the vehicles traveled 20,752 km and fired 2,592 105mm rounds.The Fort Hood tests were carried out by Squadron and Battalion type units and were intended to evaluate firepower, maintenance and logistical support and transition of the training method from the M-60 MBT to the M-1 Abrams tank. There was an exercise that lasted 3 days and was carried out by a Squadron, there was also a second exercise in which the 2nd Battalion of the 5th Regiment of the 1st Armored Division remained for 6 days in a row evaluating the logistical and operational support necessary for this type of units. During these tests the tanks traveled 41,971 km and fired 7,583 105mm rounds.The tests were complemented by several more carried out in the Yuma desert, White Sands and Alaska. The tests carried out at White Sands were of the electromagnetic type and the vehicles were subjected to neutronic and Gamma ray radiation to observe the effect on the electronic equipment. On these tests, heat and radar signatures were taken into account with a view to going unnoticed by enemy sensors. In both the Yuma Desert and Alaska trials, the general behavior of the vehicle in extreme weather environments was evaluated.The arrival of the M-1 Abrams to the US Army meant the conversion of tank platoons equipped with 5 vehicles to platoons equipped with only 4 vehicles. This was made convenient by the high cost of the new vehicle as well as the greatly improved capabilities of the new tank compared to the previous M-60 MBT. -At the end of 1988, the 1st and 2nd Armored Divisions (Forward) and the 3rd Infantry Division, all in Europe, and the 3rd Armored Cavalry Regiment at Fort Bliss, Texas had received the new M-1A1 Abrams. The replaced M-1 Abrams were shipped to the United States and delivered to the US Army’s 1st Cavalry, 2nd Armored, 1st Infantry and 24th Divisions. The National Training Center also received a few more and the rest were delivered to National Guard units in Georgia, Mississippi, North Carolina and South Carolina.The M-1 Abrams MBTs were in service with the US Army until 1996, but did not fight in the 1991 Gulf War. However, they were deployed to Saudi Arabia in August and September 1990 as part of the 24th Infantry Division (Mechanized) and the 197th Infantry Brigade (Mechanized). In fact, they were the first US Army armored units to reinforce airborne and Marine units in the area. As the months passed, all of these units, except two battalions, were replaced by other units equipped with the 120mm gun M-1A1 Abrams MBTs.Despite the excellent qualities of the M-1 Abrams MBT, it was not exported and was only used by the US Army. However, its design was used by Chrysler as the basis of the South Korean XK-1 ROKIT (Republic of Korea Indigenous Tank) project developed in the first half of the 1980s, which culminated in the manufacture of the K-1 (Type 88) MBT. Of course, nearly 3,000 Abrams MBTs have been exported, but all have been vehicles equipped with the 120mm gun.At the beginning of 1981, 14 production M-1 Abrams were equipped with a new 120mm gun (XM-256) and designated M-1E1. This modification was intended to carry out tests to be able to install this gun in all future M-1 Abrams production tanks. In addition, other improvements were included, like extra armor plates in the turret faces, the lower front hull and the rear skirt over the sprocket wheel. A bustle rack was installed at the rear of the turret for storage, and an additional storage bin was added on the turret sides. After various tests in the field, it was decided to add all these improvements, except the gun, to the production tanks, resulting in a variant named M-1IP or M-1 IPM1 (on the image).The M-1 IP Abrams (on the image) incorporated various internal and external improvements, but continued to carry the M-68E1 105mm gun as it was considered an interim tank until the arrival of the M-1A1 variant armed with the 120mm gun. In some vehicles, an NBC over-pressure ventilation system was installed, which increased the weight of the tank by 1 ton, forcing the suspension to be reinforced and adjusted. Unfortunately, this increase in weight has meant a reduction in maximum speed by 5 km/h and a reduction in range of about 15 km.During survivability tests on some tanks of this new variant, captured Soviet ammunition, missiles and artillery projectiles were used and it became clear that the protection provided by the M-1 Abrams was infinitely superior to the previous M-60 MBTs, being capable of resist direct impacts without resulting in the loss or disabling of the tank. The first vehicles were delivered to units stationed in Europe and the United States in December 1984 and the total production of M-1 IP Abrams (on the image) reached 894 vehicles, which were manufactured from October 1984 to May 1986.
