Armed Transports = Q Ships
Railways should be standard, everyone had them - not a tech
Observation balloons were standard - not a tech
Aircraft should be able to go progressively up to 4-4 (fighters should only ever move 2); you have to buy each successive advance one at a time.
Add:
Bomber [cost 8]
1(vs air)-2(vs ground)-6 (the movement can be “there and back”, i.e. you can bomb an area you’re not attacking by land, then land back in your own tt.) Bombing phase should be conducted after air superiority, before general combat.
The effect of bombing an enemy capital should be moral rather than financial, though it can be converted into a cash value (factories emptied of workers after a bombing raid).
Russia & Italy should start with this tech.
Light tank
2/3-1-1 (cost 5)
Same in combat as heavies, but does not have the “cancel a hit” ability.
Aircraft Carrier
Can carry one fighter. This plane can then perform observation for accompanying warships (need to know exactly how naval battles work).
Steel Helmets
This needs to have two types of infantry piece per side to work. After acquiring the tech, all newly raised infantry have them as standard. You can upgrade existing infantry at 1 IPC each.
Infantry without steel helmets defend on only 2, with them they defend on 3.
I would also allow copying of techs. That is:
After first building a tech, a power may pass the knowledge on to its allies, who can then each pay $5 to get it for themselves.
After first having a tech you don’t possess used against you, you may copy the tech for your own use, after paying the standard $5 fee, then pass it on to your friends after you’ve built one.
Through this system, the advantages of having a tech are reduced to just a couple of turns, after which you’re likely to see the enemy’s own version used against you. This prevents a cheesy “tech victory” against an opponent who was just unlucky never to roll a particularly useful tech.