Captain Jack (Updated: 7/15/2016):
With expediency and cost in mind, it was decided to take the existing M48 systems and modify it to suit the ever-changing requirements of the then-modern battlefield. The basic M48 was upgraded with a new, more powerful engine mated to a cross-drive transmission system and a the excellent British L7 main gun was fitted to a new turret. The hull was revised with more straight contours and aluminum wheels replaced the M48's steel ones. The general turret shape of the M48 more or less remained, though this was progressively changed to a more defined, unique form to help reduce the front and rear profiles. The resulting design came to be known initially as the "M68" but this was later changed to the more well known "M60" designation. While not officially labeled "Patton" in its formal US Army listing ("105mm Gun Full Tracked Combat Tank (M60)"), it was widely accepted as part of the Patton family that began with the "M46" - and all Pattons (M46, M47 and M48) were more or less related to the late World War 2-era M26 Pershing Heavy Tank. Initial production of the M60 began in 1959 out of the Chrysler Delaware Defense Plant to which the first M60 units were formed and stocked in 1960. Production quickly switched to the Chrysler Detroit Tank Plant in Michigan thereafter and would last until 1987 to which some 15,000 units would be manufactured. The M60 is noteworthy for becoming the US Army's first "Main Battle Tank", the Army doing away with its World War 2-era "Light", "Medium" and "Heavy" Tank classifications.
The M60 was a very conventional tank for its time - categorized as a "first generation" Main Battle Tank. The design featured a well-sloped glacis plate at the front hull with a very shallow hull superstructure. The engine compartment bulged the hull roof at the rear but was short enough to compensate for the turret overhang, allowing for a full 360-degree traverse and engagement of enemy targets at any angle. The vehicle sat on a torsion bar suspension system utilizing six double-tired road wheels to a track side. The drive sprocket was held at the rear while the track idler was at the front of the hull. Three track return rollers guided the track along the upper portions of the hull sides. The top facing of the tracks were covered over in a thin fender-type installation to which stowage atop the surfaces of the tank could be addressed as well as storage boxes applied. The turret was centrally-located atop the hull roof and sported thick, well-sloped sides for basic ballistics protection. The gun protruded over all sides of the tank in a traditional fashion. A commander's cupola clearly identified the M60 series from previous Pattons, this emplacement positioned to the right of the turret roof and could operate as a "mini" turret apart from the main turret. Armor protection measured 155mm at the thickest facing, equivalent to just over 6 inches and the hull was formed of homogenous steel. The M60 was crewed by four personnel made up of the driver, tank commander, gunner and loader. The driver was seated in the front hull at center with the remaining crew in the turret. The gunner and commander were seated to the right of the gun with the dedicated loader to their left. The loader was afforded his own entry/exit hatch. The M60 was also the last American tank to feature a floor-mounted escape hatch - something not carried over in the modern-day M1 Abrams series.
Primary armament revolved around the M68 105mm main gun (except for the M60A2 which utilized the M162 152mm main gun - this variant detailed below). Additional armament came in the form of a 7.62mm M73 series machine gun coaxially-mounted in the turret next to the main gun and operated by the gunner. This weapon allowed for engagement of "soft" targets beyond the scope of the main gun - primarily infantry, which remained a great threat to a tank, particularly at close range. At the commander's cupola was installed an M85 12.7mm heavy machine gun designed to counter threats from low-flying aircraft (mostly helicopters but also low-flying aircraft) and light armored ground vehicles. All told, the M60 could provide maximum firepower and its own defense in one complete package. Smoke grenade dischargers were later added to the turret sides while the engine could also produce its own smoke for both offensive and defensive tactical actions as needed.
The M60 weighed in at 50 short tons and sported a running length of over 30 feet with the gun forwards. Width was nearly 12 feet while height was 10 feet, 6.5 inches, a rather tallish profile for a combat tank and one of the key criticisms of the series for the life of the vehicle. Power was supplied by a single Continental AVDS-1790-2 V12 air-cooled Twin-Turbo diesel engine of 750 horsepower. This was mated to a General Motors cross-drive single-stage transmission with two forward and one reverse speeds. Top road speed was approximately 30 miles per hour with an operational range equal to 300 miles. Performance was acceptable for the vehicle but proved another long-standing criticism of the series.
As technology evolved, so too did the threats of the battlefield. As such, systems developed in the latter portion of the 1950s would soon show their age, being outmoded by newer and more efficient engineering and materials. Therefore, implements such as the M60 gradually were updated in turn, hoping to counter the threats posed by a steady stream of like-developments being reported in the Soviet Union. In 1963, the M60A1 appeared with a newly redesigned turret that was internally more spacious. Additionally, the suspension system was improved and armor protection revised for the better. This variant - produced until 1980 - was followed into service by the M60A2 - nicknamed the "Starship" - which brought along with it a very different, lower-profile turret emplacement with a very noticeable commander's cupola. Key to this production model was its implementation of the 152mm main gun, the same as found on the M551 Sheridan "air droppable" tank, making the M60 compatible with the MGM-51 "Shillelagh" anti-tank missile. The M60A2 mark was developed to fill the gap between the M60A1 and the upcoming American-German "MBT-70" project which eventually fell to naught. As such, the M60A2 was a short-lived production model for the M60A3 proved the next M60 standard and many M60A2s were converted to the A3 mark while other M60A2s became specialist battlefield vehicles such as bridgelayers. The M60A3 production designation was given stabilization and a thermal sleeve for its M68 105mm main gun, a ballistics computer for accurized engagement, a thermal sight at the gunner's position, improved coaxial machine gun functionality, an air filtration system, revised searchlight function, an improved powerplant and improved Raytheon laser rangefinder. This M60 form became the most advanced American MBT in service during the early 1980s. Additionally, the M60A3 featured external smoke dischargers along the turret sides as well as an internal smoke generation system supplied through the engine's operation (many Soviet tanks utilized this feature as well). The improvements certainly brought the M60 family line closer to the capabilities of the newest Soviet battlefield threat of the time - the T-72 Main Battle Tank - and, in some ways, still compared favorably to the more modern M1 Abrams beginning to take hold in the US inventory. The M60A3 soldiered on for the US military until 1997. Those M60A3 production forms labeled as "M60A3 TTS" marked them as "Tank Thermal Sight" - noting their use of the AN/VSG-2 thermal system.