well, we don´t have a tech tree in aa games.
there re so many interesting things to put in a techtree.
for example, germany invented a magnetic mine to be atracted to ships and sink them. England invented then a degauss of the hull that prevented magnetic mines to be atracted by the ships metal.
germany invented a torpedo that followed the noise of enemy ships, the allies invented a noise equipment to be pulled by the ship with a cable to cheat the torpedo.
the USA invented a kind of a balloon that was inside the fuell tanks of figthers and other planes so that the empty space created inside the deposit by the comsumption of fuel was not filled with explosive gases. The consequence was that was much more easy to makea zero explode than a dauntless.
usa used CO against fires in carriers that combined with O2 produced CO2. without O2 the fire could not continue burning. Japan used water that boiled with the fire and was a big mess.