Star Wars X-Wing (2nd Ed): BTL-A4 Y-Wing Expansion Pack - Rules of Play says:

Once a common sight in the Imperial Navy, the slow and lumbering Y-wing has long since been phased out of the Imperial ranks in favor of the faster and far more maneuverable TIE fighter. To the fledgling Rebel Alliance, however, the ship's durability, dependability, and heavy armament make it an appealing choice for missions that need a little more firepower.

The BTL-A4 Y-Wing Expansion Pack includes a beautifully pre-painted miniature and all the ship and upgrade cards you need to incorporate this powerful ship into your Rebel squadron. In addition, the BTL-A4 Y-Wing Expansion Pack contains a few entirely new cards that have never before appeared in the game's first edition. These new cards and associated punchboard are also included in the Rebel Alliance Conversion Kit for the benefit of veteran players!