The Rebel Alliance found great success with the deployment of hyperdrive-equipped starfighters for use in hit-and-fade attacks against the numerically superior Imperial Navy. After the Battle of Yavin, the A-wing was designed to maximize this advantage.
However, the Imperial response to this success was to deploy a large number of mid-sized ships, such as the Nebulon-B frigate, to counter the Rebel starfighter strategy. The Nebulon-B, with its tighter arrangement of laser cannons, starfighter compliment, and rapid response time to Rebel attacks made it ideal to deal with this new threat.
Admiral Ackbar, in his foresight, sought to design a counter to this Imperial response. He sought the assistance of the insectoid Verpine, in what was dubbed Project Shantipole.
This project yielded the design for the Slayn and Korpil B-wing heavy assault starfighter. It featured four sublight engines, modular energy weapons configuration, a large warhead load, and an unusual cockpit design. The cockpit rested in a bearing-lined collar which allowed it to rotate 360 degrees around its axis. This, paired with retractable s-foils designed to spread the B-wing's field of fire, created a fighter who's configuration at any given time could be quite unpredictable.
With initial deployment of the B-wing, rumors quickly circulated around the Imperial Navy that a powerful new fighter was attacking and destroying large Imperial ships. The fear had gotten so great that entire squadrons of TIE fighters were known to turn tail and run when a flight of B-wings jumped into a combat area.
B-wings were heavily armed and featured a modular weapon pod system. Typical armament was three standard laser cannon and three ion cannon, although the exact arrangement of these weapons on the spaceframe varied from squadron to squadron and from mission to mission. It also carried a large warhead load, with a dozen proton torpedoes comprising the standard payload. This mix of weapons gave the B-wing a very heavy punch and great versatility when choosing targets.
B-wings' defensive abilities lie primarily with its extensive shielding. Its shield generators were among the most powerful ever deployed on a starfighter, and protected it well against the blistering firepower it faced in assaults on capital ships. For its size, it was reasonably agile, as well, making it impossible for TIE pilots to ignore the B-wing's capabilities as a dogfighter.
The B-wing was a potent weapon system. However, it was not invulnerable. The Empire discovered that TIE Interceptors, with their quad lasers, agility, and larger numbers, were effective at countering flights of B-wings. Thus, B-wings' best defense against TIE Interceptors was escorting X-wings or A-wings.
Although it was intended to replace the aging Y-wing, the B-wing never completely displaced the older craft. Although more capable on paper, the B-wing was a complex, expensive system, and the Y-wing had a reputation for being comparatively rugged, easy to repair, and inexpensive to operate. The Y-wing had a comparatively higher mission capable rate, having been a known quantity and in use with the Rebellion for decades before the B-wing's initial deployment.Thus, the two heavies ended up serving the Rebellion side by side through the Battle of Endor and beyond.