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"To give us a better understanding of Halo Wars' units and all the upgrades available, Xbox.com posted a downloadable Halo Wars tech tree chart (PDF).The Halo Wars tech tree (not to be confused with the plantable type) is an easy-to-use reference guide that visually explains the technology progression of both Covenant and UNSC units, as well as each of their Leaders' unique powers. The chart comes in especially handy when creating the nearly invincible Grizzly and ODST combo. It's a strategy we nicknamed the \"Drop Shock and Awe.\"[Via HaloWars.com]"^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.engadget.com/2009/03/05/download-a-digital-copy-of-the-halo-wars-tech-tree/>