Most techs are useless, except forcertain players.
Rokets: If your germany you have three aaguns and three industial complexs near by. As long as your winning in africa and the US/Uk is not ready to open up another front this tech can easly fix a bad Russian front.
Jets: Well now you have a 3/5 fighter, goooood for you, But you should have just bought six infantry
Super Subs: It looks sexy on the outside put most countries don’t have enough somes for this to be usefull
Long Range Aircraft: Just not enough oppertunites for this to be useful.
Combined Bombardment: Enough said
Heavy Bombers: At some point in the game it’s not a bad idea to get heavy bombers. For an average cost of 30 IPC’s you can turn your alomst useless one dice bombers who only will cost the enemy 15 IPCs on average ( The same amount who payed to get the bombers in the first) into two dice bombers which will cost the emeny 30 IPC per bomber.
PS: If your country has an income under 30 IPCs it means your about to lose your cpaital so don’t woory about techs, buy infantry