THE MODERN BATTLEMECH
The modern BattleMech is perhaps the most complex machine ever produced. Each 'Mech contains thousands of different components, far too many to explain here. But exploring the systems and the capabilities of BattleMechs is a great way to start getting to know these marvelous machines.

Skeleton
Every BattleMech contains a "skeleton" made up of several dozen "bones." Each "bone" is a honeycombed, foamed-aluminum core wrapped with stressed silicon-carbide monofilament and protected by a rigid, titanium-steel shell. Each of these artificial "bones" has attachment points for the myomer "muscles" and servos that drive the BattleMech. This skeletal construction helps make BattleMechs less vulnerable and easier to repair than vehicles supported by stressed-skin shells.

Muscles
Two different systems are used to drive BattleMechs and control their movements. Small, electrically driven actuators move a 'Mech's light weapons and sensor arrays. Bundles of polyacetylene fibers called myomers control a 'Mech's limbs and main weapons. Myomers contract when exposed to electrical current, much like human muscles. And if a BattleMech's myomers are damaged in battle, technicians can replace the fiber bundles with new ones or "transplant" myomers from other parts of the 'Mech's skeleton. Transplanted myomer bundles cannot restore full function to a damaged limb, but they do provide limited mobility and strength.

Armor and Weapons
Two separate layers of armor provide modern BattleMechs with protection against energy and projectile weapons. Usually, aligned-crystal steel is used for an outer layer of armor. The aligned-crystal steel has excellent heat-conducting properties, and so it provides excellent protection against lasers and particle-beam weapons. An inner layer of boron nitride impregnated with diamond monofilament stops high-explosive armor-piercing (HEAP) rounds and fast neutrons. This second layer of armor also prevents any armor fragments from damaging the BattleMech's internal systems.
BattleMechs usually carry charged-particle-beam weapons or lasers as their primary armaments, because energy weapons can be powered virtually indefinitely by a 'Mech's onboard fusion reactor and do not require ammunition reloads. In addition to energy weapons, many BattleMechs carry launching racks for short- or long-range, non-nuclear missiles. Still other 'Mechs mount rapid-fire autocannons or machine guns for use against infantry, aircraft and other BattleMechs.

Power
BattleMechs require a large, constant power supply for movement and combat. The fusion reactor, which produces enormous amounts of electricity from ordinary water, is the most efficient system for providing this power. And because the fusion reaction created by a BattleMech's power plant does not release neutrons, the power plant can operate indefinitely without becoming radioactive.
The fusion plant produces electricity by a process known as magnetohydrodynamics. In this process, magnetic fields are used to channel plasma from the fusion reaction into a loop. This plasma is electrically conductive, and so the loop functions as a powerful generating coil, producing both electricity and waste heat. Every BattleMech carries radiators called heat sinks to help dissipate this waste heat. Heat sinks are especially important, because excessively high internal temperatures can disrupt the magnetic containment fields around a BattleMech's reactor. And if a power plant's magnetic "jar" is disrupted, an uncontrolled fusion reaction may occur, releasing neutrons and exposing the BattleMech's internal systems and its crew to damaging and lethal radiation.

Movement
BattleMechs can attain walking or running speeds ranging from 40 to 100 kilometers per hour in open terrain. Dense forests, swamps, and steep slopes will slow a 'Mech, but very few terrain features can stop one. In addition, many 'Mechs can jump over obstacles by superheating air with their fusion reactors and jetting it out through so-called jump jets. Jump-capable BattleMechs operating on worlds without atmospheres often carry small quantities of mercury to use as reaction mass for their jets. And all BattleMechs can move underwater when crossing rivers or small lakes.
Spaceborne BattleMechs can make assault landings from low orbit. Special reaction jets housed in their feet allow them to soft-land from altitudes of up to 320 kilometers. During re-entry, breakaway ablative shields protect a BattleMech's vulnerable sensors and weapons.

Weapons and Heat-Dissipation Strategies
Because a BattleMech's systems are pushed to their limits during combat, 'Mechs engaged in combat generate large amounts of waste heat rapidly. We've already discussed how excessive internal temperatures can disrupt a fusion reactor's magnetic containment shields. But excessive heat can also impair or permanently damage a 'Mech's electronics and computer systems, slowing the BattleMech's movement and reducing the accuracy of its weapons.
Heat sinks are one way of controlling the heat build-up in a 'Mech. But the heat pouring out of these radiators can produce strong infrared (IR) signatures, which can make a 'Mech easy to target. To solve this problem, MechWarriors have found other ways to control heat build-up. Often, MechWarriors will place their machines in shallow lakes or rivers, if possible. Through the processes of conduction and convection, the running water helps dissipate the 'Mech's internal heat, allowing a higher rate of activity. On temperate or cold worlds, the atmosphere itself can help dissipate waste heat in the same manner. On the other hand, the high outside temperatures of a desert or jungle environment can exacerbate a BattleMech's heating problems.
Perhaps the most common way MechWarriors control heat-build-up is by regulating the movement and firing rates of their machines manually or by reprogramming the machine's movement control computer and its secondary systems. These computers can be used to limit the 'Mech's rate of activity and the resulting heat build-up. For example, when a 'Mech is sent to a high-temperature world, its activity-rate setting may be lowered. The 'Mech will move more slowly and fire less often than it would on a temperate planet. When a 'Mech is sent to fight in an arctic climate, the setting is raised, allowing faster movement and a higher rate of fire. Reprogramming is usually carried out while the BattleMech force is enroute to its assignment aboard DropShips. The process takes aproximately two weeks.
Because BattleMechs are always adjusted for the expected external temperature of their combat environments, sudden increases in outside temperature can have a devastating impact on a 'Mech's ability to dissipate waste heat. Tacticians have developed a whole series of battle tactics to take advantage of this 'Mech characteristic. For example, commanders regularly set forests on fire while enemy BattleMechs are advancing through them. The superheated air roaring around the 'Mechs can overload the machine's cooling systems or drastically reduce their efficiency, thus hampering the machines' combat capabilities.