The Crab was designed by Cosara Weaponries to be a medium raider and guerrilla fighter. First built in 2719, fewer than 1,000 of this design were delivered before the outbreak of the Succession Wars. The Crab received favorable initial reports, but experts saw the 'Mech's inability to jump as a limitation on its usefulness as a raider.
         The Crab possesses good overall speed and can survive for weeks without resupply. All of its weapons are energy-based, which can make the Crab slightly hotter to operate than other 'Mechs of its class. The Crab might well have become the standard medium 'Mech of the SLDF, had events not forced General Kerensky and his loyalists to leave the Inner Sphere.
         Instead, Cosara continued building the design and sold it to the Capellan Confederation until they lost access to the higher technologies that made it function. They then redesigned the lesser CRB-20 and began building that. They could never build enough to outstrip the losses the Confederation took though, and so the Crab never became one of their primary BattleMechs. The Fourth Succession War saw Northwind joining the Federated Commonwealth and it began selling the design to them. Ironically, many Northwind Crabs fought in the War of 3039 against Crabs piloted by the Draconis Combine, where they generally cancelled each other out.
         Many more died against the Clans when they invaded, but in the 3050s memory cores with old Star League designs began to come to light. At the same time, Cosara finally decoded one of their memory cores that told them about the CRB-27b, a variant of the standard Star League Crab that had reportedly begun small-scale production before the League disbanded. The differences were minimal, and yet made the design much more powerful, and so Cosara decided to put it into production, with a few twists.

         Even the new Crab contains no new technology. Every major component on the Crab has been proven on another 'Mech design. Techs dream of assignment to a Crab, because the maintenance time is less than half that for other 'Mechs in its class. A Crab Walk is synonymous with easy duty.
         The Crab's armor protection is generally good. The arms and legs are especially well-protected, with Ferro-Fibrous Armor used throughout. Its weakest areas of protection are the left and right torsos, but even those areas can withstand a direct PPC blast without a breach.
         The 'Mech's weapons systems are the fairly new Cyclops lasers. The extended range large lasers are a matched set, housed in the claws and forearms of each arm where they provide an excellent arc of fire. For hundreds of years, pilots have had a tendency to use the older lasers as clubs, knocking the focusing mirrors out of alignment and rendering the laser inoperable. When Cosara acquired the Cyclops lasers, they buried them deep inside the arms so MechWarriors would be forced to use their claw and fists. With the Cyclops lasers being so easy to maintain to begin with, this fixes one of the few true problems of the design.
         To provide a secondary line of defense, a Cyclops extended range medium and small laser fit in the center torso and head, respectively. The medium laser is well-protected from the engine, and heat sinks allow an unrestricted flow of heat through the center torso and out of the back. The headmounted small laser is normally used only as a last resort. Ineffective at long ranges, it is best used against soft targets, such as infantry and rioting civilians. The cockpit is well-insulated from the heat of the engine and the small laser. Pilots appreciate the relative comfort of piloting a Crab.
         The 'Mech's ejection seat varies from the standard design. The pilot has two methods of escape. If an explosion is imminent, the top hatch is blown back and the seat is jettisoned through the roof of the 'Mech. Seat thrusters stabilize the descent to a controlled fall, and the pilot lands roughly 200 meters from his machine. If no explosion is likely, the seat is rotated 90 degrees and fired out the back. The pilot will land 20 to 50 meters from his 'Mech after a much shorter and gentler ride.

         Cheap, easy to maintain, fairly quick, and mounting effective weapons that do not need ammunition, the Crab is a favorite of mercenary forces across the Human Sphere. They need only provide water, and the Crab will never stop running until it is destroyed or is victorious in battle. Most units in the Allied Mercenary Command make use of this design, making it a common sight across known space.