American M60A3 tank in Lake Charles, Louisiana.
Magach 7C in Yad la-Shiryon museum, Israel.
A development contract for the new tank was awarded to the Chrysler Corporation in September 1958 and called for four pilot tanks to be constructed. The vehicle was designated XM-60 in its prestandardisation form, the ‘X’ (for ‘experimental’) sub-designator being adopted right across the board by the US armed forces at around that time. The vehicle was standardised as the 105mm Gun Full Tracked Combat Tank M60 on 16 March 1959. The main difference between its hull and that of the M48 was the profile of the nose – the M60’s was wedge-shaped instead of elliptical. The hull could be cast as a single unit or fabricated by welding cast sub-sections. The turret was invariably cast of a piece. The running gear was identical to that of the M48 except that the roadwheels were now of forged aluminium, and the hydraulic shock absorbers were deleted, bumpers being substituted to limit the travel of the first and last roadwheels. The M60 entered US service in December 1960 and remained in production until mid-1985, by which time some 15,000 had been delivered to the US Army and US Marine Corps and to many export customers. As late as the mid-1990s, the M60 was still the most numerous tank in US service. The base-model tank, with the turret from the M48A2, was superseded by the M60A1 in October 1961, and the former went out of production a year later after a total of 2200 had been manufactured. As well as the elongated turret, the new variant had detail changes to the running gear, and a steering T-bar in place of the original wheel. Adequate electronic ballistic computers were still not available, although provision had been made for one when the new turret was designed. Hull-front armour was increased in thickness in the M60A1 to 110mm (4.33in), and comparable upgrading was applied to the hull sides. The tank’s all-up weight increased from 46.25 tonnes to very nearly 49 tonnes in consequence of these changes, but no modifications were made to the powerplant. The tank’s maximum road speed stayed at 48km/h (30mph), the original vehicles having been governed to that anyway.
The committee that had originally decided on the M60’s specification in 1957, which had been chaired by Chief of Staff General Maxwell Taylor himself, had been at pains to further specify that by 1965, the US Army armoured divisions should have been provided with an alternative to conventional tube artillery. The alternative was specified as an infra-red, line-of-sight guided missile capable of subduing tanks that were so well armoured as to be invulnerable to conventional ammunition of the time. By January 1964, such a missile, the Philco- Ford MGM-51 Shillelagh, was available, and four different turrets capable of mounting a short-barrelled XM81 gun/launcher for it were available for study. The XM81 was called a gun/launcher because it could fire conventional 152mm ammunition as well as the Shillelagh. Two of the available turrets were compact designs with semi-remote operation that placed the gunner and loader down in the hull; the other two turrets were more conventional. One of the slimline turrets was chosen, and work commenced on adapting the new weapon to the M60 tank. The M60A2, as the missile-armed tank was designated, was never much of a success. It was 1972 before it entered service, and just 525 examples were constructed. All of them were fairly rapidly withdrawn and converted into, among other things, bridgelayers and Combat Engineering Vehicles with A-frames and bulldozer blades as well as a 165mm short-barrelled demolition gun.
Chrysler incorporated a not dissimilar turret to that employed on the M60A2 into its K tank design study, although it mounted a much more powerful gun/launcher, which was developed for the aborted US-West German MBT70. The XM150 gun/launcher was a more capable weapon all round than the XM81 and could fire conventional sub-calibre armour-piercing fin-stabilised discarding sabot (APFSDS) ammunition as well as launch the Shillelagh missile. However, just in case XM150’s merits were lost on the reviewing committee, Chrysler also made provision to equip the K tank with the smooth-bore 120mm Delta gun, which fired a similar sub-calibre round and was very much the shape of things to come.
At a time when the US Army (and virtually all of its funding) was absorbed in the Vietnam War, it did not much matter anyway. The K tank design exercise stood very little chance of success, even though it also had a certain innovative value in areas other than its armament. The disappearance without further trace of the K tank meant that the Shillelagh already had three strikes against it. The weapon’s installation into the ill-fated M551 Sheridan light tank was to make it a straight four in a row.
By the time the 1960s drew to a close, the M60 main battle tank was beginning to look a little jaded. In January 1970, the Chief of Staff approved a programme to substantially update it by means of what was known as product improvement. Proposals came thick and fast. Some were relatively straightforward, like the top-loading air cleaner cartridges, which extracted much more dirt from the air going into the engine and henced prolonged the mean time between replacements, and the add-on stabilisation system, which worked with the existing hydraulic turret actuation hardware.
UPDATING THE M60
Other straightforward modifications included the adoption of a new type of track with longer life and replaceable rubber pads. A new and much more reliable co-axial machine gun was also fitted, as were passive infra-red sensors, a laser range-finder and solid-state digital ballistics computer, and a thermal jacket for the gun barrel to minimise distortion caused by uneven heating or cooling. What became known as the RISE (reliability improved selected equipment) engine, on the other hand, required considerably more work, but proved well worth the expenditure.
Not all the proposed modifications were accepted by any means. One element developed for the K tank, the innovative tube-over-bar (TOB) suspension system, found its way into the M60A1E3 test vehicle but did not make the production model. The system replaced simple torsion bars with components mounted in tubes, thereby doubling their effective length and increasing roadwheel travel by 45 per cent. It was a considerable improvement over the original system, which dated from the M26. However, before the improved tank went into production, two further systems were presented. One was a simpler, and hence cheaper, method, using ordinary torsion bars forged from H-11 electroslag refined steel; the other a more complicated but even better method, using hydropneumatic units.
A hybrid of the latter two seemed set to be chosen, but in the end, the designers opted to revert to the original M60 system, even though all the improvements would have given both a better ride and enhanced cross-country performance.
M60 AT SPEED
In tactical terms, the replacement of the mechanical, analogue ballistics computer with the new XM21 electronic, digital ballistics computer system developed by Hughes was probably the most important improvement in the revised tank’s equipment. The computer took into account such factors as altitude, ammunition characteristics, cross wind (measured by a mast-mounted sensor on the turret top), cant, drift, gun jump, gun tube wear, sight parallax and target motion when laying the gun, while the tank’s laser range-finder was accurate to within 10m (33ft) at any range between 200 and 5000m (660 and 16,400ft). All this almost guaranteed a first shot hit in trained hands. The revised M60 was standardised as the 105mm Gun Full Tracked Combat Tank M60A3 on 10 May 1979, and the first unit to receive them, the 1st Battalion, 32d Armor Brigade, got 54 of them just 16 days later.
And development of the M60 series, at least unofficially, did not stop there. The engine came in for renewed scrutiny, this time vis-à-vis its performance rather than its reliability. Two straightforward variants of the AVDS-1790 were proposed – the AVDS-1790-5A developing 910hp, and the AVDS-1790-7A, which developed 950hp. Consideration was also given to a technically innovative derivative, the AVCR-1790, which developed no less than 1200hp, from the same basic unit, largely thanks to its variable compression ratio pistons. A gas turbine unit from Avco- Lycoming was also looked at, and although it was not accepted for the M60 series, it went on to become the powerplant for the all-new M1 Abrams, the MBT with which the US Army would go into the 21st century. Each and every one of these powerplants would have needed a new transmission package, since the CD-850 was close to the top of its performance envelope in dealing with the 750hp that the standard engine put out. A variety of improved transmissions were offered, both from Allison, the original suppliers, and from other sources. In the event, the US armed forces did not adopt a new power unit, although Teledyne-Continental later offered the M60AX as a private venture, with the AVCR-1790 engine and the Renk RK-340 transmission, together with National Waterlift hydropneumatic suspension. Even with 4 tonnes of additional armour, the M60AX was 50 per cent faster on the road than the other variants, and almost three times faster across rough ground, managing 38km/h (24mph) to the 14.5km/h (9mph) of the tanks with torsion bar suspension.
Israel was one of the most enthusiastic M60 users, having graduated through M47 and M48 Pattons – and M4 Shermans in a variety of guises, too, come to that. Along with improved Centurions of British origin and the locally produced Merkava, M60s were the mainstay of Israel’s armoured divisions during the 1973 Yom Kippur War and in the fighting in Lebanon in 1982. It is clear from users’ reports that the tanks performed as expected, the M60A3s proving themselves more than a match for the Soviet-supplied T-62 tanks with which the opposing Egyptian and Syrian forces were largely equipped. M60A3s proved largely equal to the few T-72s they encountered, too, although that may have been due to inept handling rather than any particular weakness in the T-72s themselves. Meanwhile, the Israeli M60Als scored well against the T-54/55s, despite the latter’s heavy armour. The Israeli Defence Forces have a solid history of improving the weapons with which they are supplied, and the M60 has been no exception. The best-known Israeli M60 ‘accessory’ is the Blazer explosive reactive armour system, which employs plates of explosive sandwiched between thin sheets of steel armour. The purpose of this explosive armour is to defeat HEAT rounds by detonating the incoming warheads prematurely on the outer armour, setting off the explosive ‘filling’, which in turn disrupts the destructive super-hot jet of gas from the warhead. Reactive armour can be defeated (in theory, at least) by tandem HEAT projectiles with multiple warheads, and it serves no purpose whatsoever against kinetic energy AP rounds, which just go straight through.
However, it is certainly effective against infantry armed with AT guided weapons – a source of considerable danger to a modern armoured vehicle.
In addition to going to form gun tanks, M60 chassis were also used as the basis for the M728 Combat Engineering Vehicle (as has been noted, many of the unsuccessful M60A2s were thus converted), and some gun tanks also received simplified bulldozer blade installations so that they could construct hull-down firing positions for themselves. Mine ploughs similar to those fitted to earlier generations of tank, although rather more effective on the whole, were routinely available to M60s, and mine detonating rollers have also been fitted.
More than 400 Armoured Vehicle Launched Bridges (AVLBs) have been constructed on M60 chassis. Such AVLBs can span a gap of more than 20m (66ft) and can support the weight of a fully loaded tank. They can be positioned in three minutes and recovered, from either end, in 10–20 minutes, depending on conditions. Many of the improvements brought into the M60 programme also found their way into the M88 Armoured Recovery Vehicle, including the AVDS- 1790 engine. By the time the M60 appeared, it had ceased to be truly feasible to construct SP guns on tank chassis, although the M48/M60 chassis did form the basis for the M998 ‘Sergeant York’, the DIVAD (Division Air Defense) AA tank projected to replace the M42 ‘Duster’. The M998 had a radar fire-control system based on that found in the F-16 fighter-bomber and twin 40mm Bofors cannon capable of a combined rate of fire of 600 rounds per minute. The tank took a long time and cost many hundreds of millions of dollars to develop. When it was apparently ready to be issued, belated testing under more realistic conditions than had been previously applied revealed it as entirely inadequate, and the M998 was withdrawn before it ever entered service.