Asking questions is a big part of wargaming...
1) In the 1915 scenario what is the earliest you can pull units from the eastern front transit box and put them on the line? Would this be during the Summer 1915 reinforcement phase?
This depends on whether you're playing the basic game or are using optional rules. Without any optional rules, the earliest you can pull them out is reinforcement phase of Summer 1915. If you are playing with optional rule 17.12.2 OPTIONAL GERMAN WEST FRONT "REINFORCEMENTS" the earliest they can return is in the reinforcement phase of Winter 1915-16 and Spring 1916, as the optional rule directs.
2) During what phases(s) are units moved to the eastern front transit box?
The Movement Phase of a German Player Turn. Even a Pass Move can be used to do this.
3) Can a cavalry unit conduct Raiding Fire against a fort as long as there are no enemy infantry or strosstruppen present?
Yes. This one always makes the grognards roll their eyes in disbelief. Please see page 31 of the rules for the Design FAQs. Look under the question heading, "What have you been smoking?"
Thanks in advance for any help.
My pleasure, Brent. Enjoy!