The M577 Armoured Personnel Carrier or M577-APC evolved from the Marine 70 battlefield deployment strategy, which proposed a requirement for a low-cost lightweight APC capable of being transported into combat aboard a dropship. Designed as a multi-role vehicle within a lightly-equipped rapid-reaction force, the M577 is mobile and well armed. However, the rigid design restrictions and compromises imposed by the need to be drop-transportable have resulted in a lighter, less capable vehicle than other APCs currently in US service.
EquipmentEditThe driver's view is limited to a forward window of quartz armoured crystal, though this is supplemented by periscope ports providing vision to the sides and forward quarters. Multi-function screens by the driver's and section commander's positions present a sensor-fusion display of the tactical zone around the APC. The sensors can be activated by the driver, or from the Tactical Operations Centre by the section commander. A sensor cluster is mounted with the main searchlight and can be played across a 270 degree zone in front of and around the APC. The cluster comprises a turreted thermal imager, TV optics with magnification from x4 to x20, a UV detector and an ultrasonic motion tracker. Millimeter-wave targeting radars mounted in the forward gun cupola and the main turret can track targets acquired by the main sensors, or may alternatively use their own ground-mapping and search functions to acquire targets. The effective tracking range of these radars against man-sized targets is approximately 3000 metres in open terrain. The sensors are supplemented by a forward mounted white-light and infrared searchlight for the active illumination of targets.
Structure and SeatingEditBecause of the USCM requirement that the vehicle's combat weight be kept below 15,000 kg, the M577's components were designed to be as lightweight as possible. The chassis chosen for the prototype was based on that of the M570 family of wheeled vehicles which, in the late sixties, was being developed for use in a variety of roles, mainly as a prime mover and mortar platform. The APC is built around a 4 x 4 wheeled layout, powered by a 286 kW multi-fuel gas turbine engine which generates a power-to-weight ratio in the region of 19.7 kW/kN. Although the wheeled configuration does not give as rugged a cross country performance as a tracked vehicle, it does offer considerable savings in terms of weight penalties and reliability. Each of the massive 159 cm diameter wheels receives power independently from the engine via a fully automatic, electronically-controlled transmission system. The tires are armoured against small-arms and splinter, and their pressure is controlled by a central regulation system. This allows the driver to reduce the vehicle's ground pressure over soft terrain by deflating the tires, whilst still being able to re-inflate them for road travel. The M577 has a top speed of approximately 150 km/h. The M577's chasis is made of bonded titanium and incorporates a 5 cm foam-packed floor cavity to protect against forged-fragmentation mines. Ground clearance is normally only 22 cm, but the vehicle employs a hydro-pneumatic, fully active suspension to allow a clean ride over rough terrain. The suspension is capable of boosting clearance by a full 30 cm and allows the M577 to comfortably tackle vertical obstacles up to 0.5 m. The hull is made from welded light alloys and is latched and bonded (rather than welded) to the chassis in order to prevent fatigue and failure from piezo-electric effects associated with an alloy-titanium interface. The inside of the hull is lined with boron carbide ceramic tiles, each of which has been coated with a polymer resin to prevent cracks or shattering during normal travel; this resin is 2 mm thick on the outward-facing surface of the tile and is said to provide limited ablative protection against pulsed lasers. The tiles are backed with a thick layer of woven fire resistant polymer armour to limit spalling in the event of a hull penetration. Because of weight restrictions, the armour is very light. It is capable of defeating fragmentation, small arms rounds and low-velocity armour penetrating ammunition such as rifle grenades; however its ability to stop dedicated tank-killing weaponry is light.
The M577 carries a formidable array of weaponry in support of its infantry complement. It can either carry one of two front weapon alternatives both housed in a hull mounted cupola covering the APC's forward area. The first alternative is twin synchronized Republic Electric RE700 20mm gatling cannons. The Republic Electric RE700 20mm gattling cannon is supplied by a 1700 round multi-feed ammunition dispenser which offers a selection of High Explosive Armour Piercing and 'Beehive' type Anti-personnel Fletchette (APF) rounds at the flick of a switch. These caseless rounds carry no propellant and are fed mechanically into the revolving chambers which are then sprayed with hydrogolic binary propellants which ignite and launch the round . Binary propellant systems are rare at this calibre (the only other such system in Colonial Marine service is the 25mm GAU/113 aboard the UD-4 dropship), but aboard the M577 this system offers substantial weight, rate-of-fire and reliability advantages over a standard caseless weapon and provides effective anti-personnel support for the APC. The only drawback of the weapon is that it is mounted to cover only the vehicle's forward arc, traversing between 60 degrees left and right of axis, and cannot be fired from a hull-down position. The second weapon option mounts a twin Lase Cannon, which has a very high rate of fire and is an extremely effective anti-personnel weapon. The M577 also houses an Automatic Light Mortar, which is mounted on the roof of the vehicle and is generally used against opponents in good defensive positions. There are 32 rounds for the weapon stored in the APC. The M577's main weapon system is turret mounted (see below for different weapon variations), allowing the APC to fire from the safety of a hull-down position. The turret assembly is fully traversable, self contained (including ammunition and power supply) and is carried on a rail track which runs down the rear of the vehicle. Geared electric motors run the turret along the track and allow it to be depressed to the APC's rear, reducing the vehicle's headroom so that it may be carried inside a shuttle or dropship payload bay. The weapons are stabilized within the turret for firing while on the move and can be elevated and depressed between +85 and -7 degrees. Hydraulic rams on either side of the turret can tilt it up to 15 degrees in all axis to provide additional elevation or maintain a level firing platform for the weapons. Target acquisition and weapons control are controlled by the section commander from the Tactical Operations Centre; however, independent targeting automation systems (or manual targeting control) can handle these functions so reducing the commander's workload. Additional armament stored in the M577 includes 7 cannisters of CN-20 Nerve Gas, 4 x M20 Claymore mines (two per M8 bandoleer), 2 x M41A Pulse Rifles, 2 x M240 Flame Units & 4 x UA 571-C Sentry Systems.