M155 Heavy Tank

The M155 Heavy Tank - Officially, "127mm Gun Full Tracked Heavy Tank, M155" - is a heavily-armed and armored tank under production by Detroit Arsenal Tank Plant in the United States to replace the aging, under-gunned and under-powered M103 Heavy Tank.

Design
The M155 is intended as the counterpart to the Russians' Iosif Stalin series of heavy tanks. This was not the result of a lack of American equipment capable of engaging the larger Russian armor - the M70 "beastkiller", with its massive 155mm cannon, was more than capable of doing so - but rather a desire for heavy armor that could act as an effective "battering ram" in tank assaults.

Revisions to, and subsequent mass production of, the M155 design were borne out of the lessons learned during the disasters of Operation Coca-Cola, where American forces suffered massive casualties and a crushing defeat attempting to break entrenched Russian positions. The purpose of the M155 is to drive enemy forces out of heavy fortifications as well as to provide long-range fire support to advancing M60s, in a similar vein to the M70.

The main armament of the M155 is a tank version of the "127mm Heavy Gun M144", the principle anti-tank gun of U.S. forces (lighter weapons having been replaced by M65 Assault Guns). This particular version of the weapon boasts a 56-calibre barrel, making it shorter than the current L/64 model but longer than the original L/42 model of the anti-tank gun. Such a huge cannon protrudes past the front of the vehicle to a considerable degree, requiring astitute handling on the part of the crew to keep it from being buried in the ground.

Dimensionally, the M155 is considerably larger and heavier than the Russian IS tanks (which, in the style of all Russian tank designs, are as small and compact as possible to maximize armor thickness for the least possible amount of weight). Due to its size, the M155 is incapable of crossing many bridges. This is not generally a significant problem, however, because the highly-motorized / -mechanized American Army almost always has deployable bridging equipment on hand. In a pinch, the M155 can simply fit a snorkel system and drive right through the river bed.

There is a bit of a running competition between crews of M155s and M70 Heavy Assault Guns to see who can destroy more enemy armor, as both vehicles are more than capable of wiping out a Russian T-55 tank through the thick frontal armor from any range at which they can hit it. However, the M155 offers several advantages over the monstrous M70. It is lighter, faster, has a rotating turret and a two-plane gun stabilizer - making it capable of firing with reasonable accuracy even while moving at maximum speed over reasonably rough terrain. The superior rifling and propellant of its gun (which is also larger by 5mm) outranges the 122mm D-25s of the IS-10 by a comfortable margin and, despite being quite a bit heavier, is considerably faster thanks to its superior powerplant. It is, however, a significantly larger target.

Advanced Features
The most obviously-unusual equipment of the M155, which it shares with the M70 Heavy Assault Gun, is an advanced optics/rangefinder package, mounted on the right side of the turret. This system, called OPTAR - or, M253 Optical Tracking, Acquisition and Ranging - is a cutting (if not bleeding) -edge development from the already high-tech Vampire night-vision project, using pulsed beams of infrared light and a powerful all-electronic fire control computer to accurately determine the range to a target even at extreme distances. With this system, the M155 is capable of scoring effective kills on enemy armor, vehicles and positions from ranges which were previously unheard of. However, despite the use of multiple high-quality ruby-inlaid lenses and filters to focus the light beams, the OPAR system will give multiple range returns in extremely bad weather (e.g. rain, snow, dust-storms) and be essentially useless, necessitating the inclusion of the standard M24 coincidence rangefinder package as well. For more information on the OPAR system, see:  http://ruffles.wikia.com/wiki/%22Vampire%22_Night_Vision_Systems#OPTAC_Fire-control_.2F_OPTAR_Rangefinding_Systems

A perhaps more important feature of the M155 is its unique siliceous-cored armor: the world's first instance of mass production approved composite armor. The principle behind the siliceous-cored armor is that the theoretical stopping power of glass actually exceeds that of steel on a thickness basis - in some cases being as much as twice as effective. Of course, glass is also extremely inflexible and thus brittle. The Americans' siliceous-cored armor has five layers: outer shells of normal Rolled Homogeneous Armor containing two inner layers of fuzed silica glass - padded with Ensolite foam - sandwiched on either side of a thinner central steel plate.

The  siliceous-cored armor offers protection which is as much as 40-50% better than pure steel against shaped charge munitions such as RPG rounds and conventional armor-piercing explosive shells. The effectiveness against kinetic energy-based armor penetrators (such as American APDS - or Armor-piercing, Discarded Sabot - rounds) is unchanged from that of regular Rolled Homogeneous Steel armor. However, Russian forces do not currently field advanced kinetic energy projectiles. The moCst advanced rounds in the Imperial arsenal are APCR (Armor-piercing, composite-rigid) projectiles, which are normal shells equal in calibre to the gun they are fired from but with a small-diameter tungsten kinetic penetrator at the core. These are much inferior to the American APDS rounds, as their light weight compared to their size makes them ballistically poor and almost completely useless at long ranges. As such, normally Russian armor employs old-fashioned APCBC (Armor-piercing Capped Ballistic Cap) explosive shells.

Production History
Designed: 1958-1960

Produced: 1960-present

Manufacturer: Detroit Arsenal Tank Plant, Chrysler Group

Specifications
Weight: 72 Tonnes metric / 79 Short Tons

Length, overall: ~12 meters / 38 feet

Length, hull: 7.72 meters / 25.33 feet

Width: 3.755 meters / 12.34 feet

Height: 3.18 meters / 10.4 feet

Track Width: 800mm / 31.5 inches

Crew: 6 (Commander, Gunner, Loader, Loader, Driver, Radio Operator)

Armor: 250mm / 10.9" maximum

Main Armament: M145A2 L/56 127mm Rifled Gun

Secondary Armament: Engine:   Dietroit Diesel 8V-71T 9.3L Diesels (530 hp) x 2
 * .50-calibre M2 Browning Heavy Machine Gun on pintle mount - radio operator's hatch, front hull, left side
 * .50-calibre M2 Browning Heavy Machine Gun on pintle mount - commander's cupola, center rear turret
 * Colt Mk. 12 20mm automatic cannon in coaxial mount - main gun mantlet

Suspension: Torsion Bar

Ground Clearance: 500mm / 21.8"

Operational Range, without external tanks: 300 km / 186.4 miles

Road Speed: 50 km/h / 31 mph