Microsoft Game Studios (now Xbox Games Studios) have a history of formulating and documenting various detailed manuals and help reference files for many video game titles they have published.
Urban Assault is not an exception. A comprehensive compendium of Help section is available as a part of the official game data. Many information about the game can be also directly found in there.
The Help files contain numerous essential and fundamental information about the game in an accessible and organised manner. However, some sections may not be fully up to the date compared to the final version (Vehicle & Building sections in particular). Still, it is an official source of the game knowledge and therefore it is highly recommended to check it in conjunction to the UA Wiki.