The term "Arm Slave" is the shortened form of Armored Mobile Master-Slave System. They are largely humanoid powered suits operating in a semi-master–slave system to coordinate with the pilot (aka master). It is one of the sum achievements of many different pieces of Black Technology. In a way, it can be said that all black technologies were created in this fictional universe to rationalize the existence of these humanoid combat machines.
In the first series, they are manufactured and used by the majority of First World nations' armed forces revolutionizing the meaning of the term "mechanized infantry". Nations confirmed as manufacturing Arm Slaves include the United States, Germany, USSR, France, and Japan. The most advanced of these units are used by the unknown terrorist organization, Amalgam, and the elite mercenary counter terrorist organization Mithril, of which the primary characters are members. Sousuke Sagara, Kurz Weber, and Melissa Mao are all Arm Slave pilots.
Arm Slaves occupy a similar cultural position to modern combat jet aircraft. Names and general information are well publicized and are a matter of public record. And like combat aircraft, detailed specifications and capabilities are kept classified. The Arm Slave has however captured the popular imagination, and even extremely advanced units such as the XM9 (M9) Gernsback have some civilian recognition through the media.
It is noted that the Arm Slaves of the Eastern Bloc have been given NATO reporting names, very much like the real-life aircraft and missile systems. The names given to the Soviet Arm Slaves, Shamrock, Savage, and Shadow indicate Arms Slaves are designated with the letter "S". This letter is shared with anti-tank and surface-to-surface missiles.
Dialog in episode 1 of the anime series indicates that periodicals, such as Jane's Arm Slave Recognition Guide, are published about Arm Slaves that contain detailed information useful even to the specialist pilots. These are considered to be Arm Slave equivalents to magazines such as Combat Aircraft Magazine published by Ian Allan Publishing and Jane's Fighting Ships published by Jane's Information Group.
These publications are purchased regularly by characters such as Shinji Kazama, but the publications, like their real world counterparts are specialized and niche products with limited mass market appeal.
The only trace of the Arm Slave present in the series Full Metal Panic? Fumoffu is a miniature Arm Slave developed by Sousuke Sagara. Sousuke's Bonta-kun units however have several comedic flaws.
The Arm Slave is a development of the Reagan Administration Strategic Defense Initiative's research in the 1980s into powered exoskeletal suits to increase the ground soldier's combat capability. Called the XM3, the first powered suit was nothing more than a powered exoskeleton sized around 2 meters tall. This proved to be of low combat effectiveness as it offered little advantage in protection in exchange for its limited mobility. This early prototype was hampered by the lack of a suitable power source that did not burden the unit past its useful load.
The designers took an unorthodox approach in the development process at this point. While technology usually is refined to become smaller and more compact, the successor XM4 project took an opposite direction. By increasing the size of the suit from 2 meters standing to around 8 meters, the designers were able to change the power source from an electrical battery system to internal combustion engines. With the advances in material sciences and engineering at the time, the tremendous increase in power-to-weight ratio of diesel engines and the artificial muscles constructed from electroactive polymers (EAPs) (later refined and called Muscle Packages) made the XM4 a viable weapons platform with a sizable payload. By increasing the payload of the powered armor, and expanding the capabilities of the unit by various electronic warfare packages and options the first generation, and inaugural Arm Slave was introduced to the world as the M4.
One of the most notable aspects of the development of the Arm Slave is the curiously short development span. It took only three years from start of the XM3 project to the resulting M4, an unheard of development span in weapons technology when equivalent civilian robotics was struggling with bipedal motion. The unnatural advance in technology was attributed to extraterrestrial sources by some publications, and managed to fuel a new generation of conspiracy theorists. Soon, the explosive evolution of the Arm Slave in the battlefield reduced its prominence to just another high tech weapon system, alongside the cruise missile and stealth jet fighters.
The M4 was the first-ever military Arm Slave. With the technology still in its infancy at the time, the M4 only found limited use in ambushes or urban combat. Military doctrine regarding Arm Slaves at this time was still immature, and more focus was placed on testing the limits of the newfound technology.
The M4 is markedly slower in response time than the average second generation Arm Slave from its dependency on mechanical and hydraulic propulsion. The Muscle Package did not exist in the current form of modular bundles. This led to an extreme difficulty in maintaining the effectiveness of the polymers as they degraded. Combined with simplistic joint anatomy, the low-powered primitive EAP "muscles" did not allow for the M4 to exhibit flexible motion or fast response and agility. However, the M4's general utility and ability to cross varying terrain while retaining combat effectiveness gave the United States enough reason to further refine the Arm Slave.
The First Generation Arm Slave is obsolete at the beginning of the story of Full Metal Panic!, and has been completely replaced by the Second Generation Arm Slave.
The USSR had joined the United States in using the newfound technology. It is assumed that the USSR was also the first ones to field the Arm Slaves later classified as Second Generation. One of the earliest units of this type is the Rk-89 "Shamrock" and later, the Rk-91 and Rk-92 "Savage". These machines stand at roughly 10 meters tall, and were initially powered by diesel piston engines, later upgraded to high-efficiency gas turbine engines. The new weapons found new use as all-weather, all-terrain ground fighting vehicles. The ability of these machines to cover any terrain at speeds above 100 kilometers per hour, and the flexibility in armament from the manipulator arms cemented the position of these machines as king of ground armored fighting vehicles. This allowed the USSR to win the war in Afghanistan (Helmajistan in the anime). Spurred by the victory of the USSR in the Afghan Theater of war, the United States developed and fielded its own advanced Arm Slave, the M6 Bushnell.
The M6 Bushnell and the Rk-92 Savage are the best known examples of the second generation Arm Slave. Joining them is the German "Drache", English "Cyclone", the French "Mistral II", and the Japanese "Model 96". These have been found stationed around the world in numbers equal to tanks.
What separates them from the first generation models is the largely the use of the modern Muscle Package to impart the Arm Slave with both fast response time and precision movement. Advancements in vetronics (vehicle electronics, a ground based equivalent to avionics) and general engineering are also counted as Second Generation improvements. The M6A1 is notable for being the first Arm Slave to be equipped with an ECS. From shortfalls in generator output, these units are built with binary drive systems combining hydraulic mechanical systems with Muscle Packages. Second Generation units are also notably loud, as their gas turbine generators emit a tremendously loud howl when running.
The Third Generation Arm Slave is exemplified in the M9 Gernsback, the first of its kind. It was thought that MITHRIL was the only organization operating Third Generation Arm Slaves in combat by its Response Teams. The same M9 Gernsback is officially undergoing OPEVAL (operational evaluation) by the United States under the prototype designation of XM9. The Zy-98 "Shadow" is the USSR equivalent and is in limited production as of the beginning of Full Metal Panic. The Plan1056 Codarl and ARX-7 Arbalest, both utilizing the Lambda Driver, are Third Generation Arm Slaves fielded by Amalgam and Mithril, respectively. Additionally, the Codarl frame is based on the Zy-98, while the Arbalest is based on the M9. Later in the events of the episode "Get Together and Make My Day", another type of Arm Slave called the Eligor appears, based on the design of Codarl, and which is even more powerful than Codarl and M9. It is unknown if the type is still classified as a Third Generation Arm Slave, however.
Powered by a lightweight and high-power palladium reactor, the M9 Gernsback features pure Muscle Package drive mated to complex joints that far closer mimic the flexibility and mobility of the human body. Although not obvious, the M9 Gernsback uses lessons learned from insect and animal physiology. Its legs are roughly modeled after a grasshopper and cat joints in construction. These developments allow the M9 to execute its tremendous leaps and absorb the shock of high drops.
The Gernsback's transition to sole Muscle Package propulsion vastly increased the power-to-weight ratio. For comparison, the palladium reactor on an M9 Gernsback is rated at 3,300 hp (2,500 kW) in comparison to the 1,200 hp (890 kW) of the Rk-92 Savage diesel generator. At the same time, an M9 only weighs 70–80% as much as a Rk-92, depending on weapons loadout. With an output more comparable to a jet aircraft, the M9 is capable of punishing maneuvers that can easily injure, disable or kill the pilot. Use of the ECS combined with the very quiet operation of the palladium reactor and the Muscle Package renders the M9 extremely difficult to detect. It is often said that the Arm Slave has reached the man-machine limit, and cannot be improved in mobility. The increased power is instead used to increase the payload capacity of the craft without affecting combat effectiveness.
The increased payload has allowed the installation of an array of electronics including advanced vetronics, fire control systems, damage control, ECS, ECCS, and electronic warfare modules tied together under advanced artificial intelligence. This has allowed for the individual Arm Slave to be a powerful command and communications platform while allowing the pilot to concentrate on combat.
The abilities of the Third Generation Arm Slave are shown in less threatening experiments. For example, two M9s are exhibited practicing the tango under autonomous operation. This experiment requires and shows the flexibility and agility of its complex joint and internal physiology, while highlighting the capabilities of the AI systems controlling the craft in complex interaction and motions. These could never be found in an older Second Generation RK-92 or Bushnell model.
An Arm Slave is operated in a semi-master–slave system. This is an operating method which has the slave arm (machine motion) trace the movements of the master arm (pilot motion). The Arm Slave is not a complete master-slave piloting arrangements, as full motion tracing is impractical within the limited space of the cockpit. This limitation is solved by the Arm Slave amplifying the motion of the pilot. The "semi" designation of the piloting system refers to this machine-assisted motion management.
The simplest and most obvious aspect is the Bilateral Angle, or the BMSA. BMSA is the amplification factor of the master movement by the slave trace. With a BMSA of 3, a pilot motion of 30 degrees is amplified to 90 degrees. Lower BMSA values are used in training, and more accomplished pilots make use of higher values. The usual range is between 1.3 (training) to 2.4 (standard) to 3.5 (high).
While the Second Generation Arm Slaves were limited in joint flexibility and overall anatomy, Third Generation units are mechanically capable of motions difficult or impossible for humans. A full master slave system, perfectly tracing the motion of a pilot would be limited to the same capabilities of the pilot. The semi-master–slave operation, controlled by complex software systems commonly called motion managers are capable of translating pilot motion into maneuvers impossible by the human body.
Skilled pilots spend a significant amount of time in optimization and personalization of these motion patterns. Arm Slave vetronics including the motion managers form a critical component of arm slave performance characteristics. The M9 AI systems are indispensable in controlling the Arm Slave, allowing the pilot to make use of the full capabilities of the craft.
THEM Anime Reviews has noted that the Arm Slaves, like most real life vehicles, are done meticulously that fans of mecha series would "online catalogues for tech books and sketches." Bureau 42 says that the "mecha[Arm Slave] action in the show is very well done. While I can’t compare the action with other more grounded mecha shows like Patlabor, the combat is very well done and easy to follow, and visually interesting." Triforce commented that Arm Slave battles in the Full Metal Panic! series would be able to keep viewer's attention to the show. Anime Chaos praises the 2D and 3D CG done on the 1st Full Metal Panic! season, with emphasis on the use of CG for the Arm Slaves.
Negative criticism has surfaced on the role of the Arm Slaves throughout the Full Metal Panic! series. For instance, Ender's review states that their mecha roles are confusing that the Arm Slaves are both "08th MS Team soldiers and Dragon Ball Z-type fighters, hurling energy balls at each other and going "Super Saiya-jin." Anime Database rated the Full Metal Panic! series 4 out of 5 because of the Arm Slaves battles since they start out from being good to being very unrealistic. GameSpot Union comments on the relationship between the Arm Slaves and the animation done on Full Metal Panic!, saying both animation and camera views were bad.