From back of book:
In 3049, the first clan forces appeared in the Inner Sphere. Armed with advanced technologies of a long-dead age, the warlike invaders unleashed a devastating blitzkrieg, capturing world after world until a total Clan victory seemed certain. Unable to match the enemy's superior 'Mechs, the Inner Sphere militaries increasingly turned to the combat fleets for relief, only to find the skies filled with deadly Clan Dropship, Jumpships and Warships - massive vessels not seen in the Inner Sphere for hundreds of years. Now the Great Houses have begun to rebuild their own armadas and stand ready to challenge the Clan invaders in the infinite battlefield of space.
The BattleTech Technical Readout: 3057 contains descriptions, illustrations, and full BattleSpace statistics for the latest Inner Sphere and Clan Dropships, Jumpships Warships, small craft, aerospace fighters, Omnifighters and conventional aircraft. BattleSpace rules clarifications and record sheets are also included.