Ok I got it to work for me. Thanks for the tips. I used 3 rifle divisions to form a rifle corps. My next quest is to find out if a regular rifle division and a guards rifle div. can be built up to a rifle corp. All units in this scenario are from the same HQ. I also wonder if ski regiments and mountain regiments can be combined with regular reg. if they are all rifle regiments.
Here are the different unit build-up / breakdown rules:
7.5.3.1. Soviet Buildup and Breakdown Availability
The Soviet ability to buildup or breakdown units is determined by date and type of unit as follows:
Rifle Division (22 June 41): Two or more rifle brigades can buildup into a rifle division. Note that Soviet rifle divisions may not breakdown into brigades. Naval brigades cannot buildup into divisions. See below for buildup of airborne brigades.
Cavalry Corps (December 41): Three cavalry divisions can buildup into a cavalry corps. A cavalry corps can be broken down into three cavalry divisions.
Tank Corps (April 42): Three tank brigades can buildup into a tank corps. A tank corps may be broken down into three tank brigades (designated 1/2/3), but may only be built up again if all three are in the same hex (7.5.3.2).
Guards Rifle Division (March 1942): Three Airborne Brigades can buildup into a rifle division, which will automatically be given Guards status. Airborne brigades may not buildup with any other type of unit.
Rifle Corps (June 42): Three rifle divisions or two rifle divisions and one rifle brigade can buildup into a rifle corps. A rifle corps may be broken down into three rifle divisions (7.5.3.3).
Mechanized Corps (September 42): Three mechanized or motorized brigades can buildup into a mechanized corps. A mechanized corps may be broken down into three mechanized brigades (designated 1/2/3), but may only be built up again if all three are in the same hex (7.5.3.2).
Guards Airborne Division (January 1943): Three airborne brigades can buildup into an airborne division, which will automatically be given Guards status. Airborne brigades may not buildup with any other type of unit.
v1.03 Beta 2 - January 21, 2011
Naval Rifle Brigades may be used to create Rifle Corps.
Restricted Soviet Rifle brigades so they can't merge into Rifle Divisions prior to May-1942.
v1.06.22 - November 29, 2012
Heavy Tank Brigades may not be used to form Soviet Corps.