The year is 1930, and the tech will remain the same as the Earth in that year. Plan accordingly. It will be generally decided by players when tech will advance a year, and conversely the year will advance a year, thus carrying on the non-time driven gameplay aspect. Up until 1940, rocket research will be in primitive stages, and airplanes will be coming into being in their own right. Tanks are being developed slowly, but the world is still torn between fast moving, lightly armed tanks and slow behemoths with large guns and thick armor. Some have even speculated about "land battleships".
Any ridiculous tech will be cited. Generally the citation will come in bright red letters as to not miss it, and because everyone likes red
Basically, if the project is cited, it means it's ahead of the timeline, or there's no way in hell any country could afford it.
The utmost liberty will be given with designs, and will only be cited if they are inherently ridiculous (Flying aircraft carrier), or out of our current tech reach (Smart bomb).
3D models, 2D pictures, sketches, etc. are highly encouraged because everyone likes pretty things.
