M901 Main Battle Tank

The M901 is the current main battle tank of the UNSC Army and Marine Corps, and successor to the M808 Scorpion widely used during the Human-Covenant War. The M901 design was first presented to the UNSC by Russian AFV manufacturer Uralvagonzavod in late 2552, as its entry to the newly initiated Primary Armoured Ground Combat Vehicle programme. The M901 design was chosen indefinitely as the successor to the M808 by mid-2553, and Uralgonzavod was contracted for mass production of the vehicle by the end of the year. The M901 main battle tank officially superseded the Scorpion as the UNSC Defence Force's primary MBT on 1 January, 2554.
==History==
==Design==
The design of the M901 is relatively exotic compared to most current UNSC armoured fighting vehicles, aside from the M808 which it replaced. The M901's own design is based on that of the Scorpion, featuring a low-profile turret mounted far back on the hull, and tracks on four articulated bogies. These external similarities, however, disguise the larger changes between the two vehicles. The M901 features a conventional fighting compartment rather than the Scorpion's 'cockpit-like' single seat. Inside the main compartment, the driver's position is located to the center and left, while the gunner is located in the center right. Both the driver and gunner sit in the center of the turret ring, a position which reduces pitch input to the crew, and allowing them to drive more comfortably at higher speeds. Forward of the driver and gunner area is the engine compartment, resting along the midline and centre of the tank and providing the best balance for the vehicle's suspension. This compartment is separated from the crew area by an noise-insulating and fireproof armoured bulkhead, and also houses the transmission, steering and braking systems.
Inside the one-person turret, the tank commander sits beside the autoloader, from where he can provide repairs or manually load the gun in the event of damage or an autoloader failure. This provides continued survivability even after loss of the autoloader in the more vulnerable turret, compared to the driver or gunners' compartment. The commander can, in the event of the autoloader being disabled, hand load the shells, decreasing the tank's capabilities but maintaining the lethality of the main gun at full capacity.
At the very rear of the tank is the combined exhaust and radiator compartment, which provides a significant reduction in the vehicle's thermal signature, and allows for better protection of the fighting compartment. As such, a strike to the armoured rear of the vehicle is not generally a lethal hit; though it can potentially lower the tank's capabilities, the vehicle would most likely still be capable of maneuvering, returning fire and such long enough to retreat to safety.
==Armament==
The M901's primary armament is its single 7A27M cannon, a high-velocity, smoothbore, 120 millimetre gun, mounted within and occupying most of the space inside the main turret. A significant improvement over the M808's 90 millimetre gun, the 7A27M's increased calibre is reflected in significant improvements in range, penetrative power and lethality. The 120 millimetre shell's higher muzzle velocity improves penetration of the target, allowing for noticeably increased damage, especially when Covenant vehicles such as the Wraith and its variants were concerned. In addition, the round produces a flatter ballistic trajectory, which allows the gun to remain accurate over a longer distance. Inside the one-man turret is the main gun and its gun mount, which fits both the main gun and the coaxial autocannon. The mount is stabilised on two axes and provides a completely stable firing platform while moving at up to 70 kilometres per hour on open terrain, and a suitably level platform up to the M901's top speed of 95 kilometres per hour. Behind this is the autoloader, which is capable of reloading the gun in under five seconds from the magazine. The M901's magazine is located in the turret bustle, and holds up to sixty shells. The autoloader system, though fully automated in basic ejection and reloading operation, is monitored by the main gunner. Using this system the gunner is able to control, by means of integrated RFID tags, round replacement, unloading, misfire ejection and loading of specific munitions types from the magazine.
During firing, the gun's breech is sealed by a vertical sliding breechblock, which is fully controlled by the autoloader system but can, like reloading, be accomplished manually in the event of a power failure. The autoloader compartment, as well as the magazine, are protected by a series of blow-out panels that prevent an ammunition explosion from destroying the fighting compartment. The M901's turret is significantly larger than that of the Scorpion, accommodating, in addition to a crew member, larger main and coaxial guns, improved autoloader and stabilisation mechanisms, an expanded magazine and bustle, and enhanced ballistic and plasma resistance. Despite this size increase, it is capable of faster traverse than the Scorpion's turret, as well faster elevation through a similar range of elevation. The gun's thermal sleeve both protects it from the elements and minimises its thermal and RADAR detectability. The bore evacuator, located approximately halfway down the barrel, features a 'dual-purpose' design, preventing propellant gases from entering the fighing compartment, and additionally using some of this gas as a buffer to absorb recoil.
==Armour and Countermeasures==
==Engine==