Not just from a realism perspective, but a gameplay one, too. The realism items have been done to death, but I'd like to point out some very serious gameplay problems with the current setup: Flight's current position in the tech tree means that planes arrive LONG before any non-plane counters come on-line. This would be like if horsemen came almost a full era before spearmen and could only be fought by other horsemen until then. Imagine how broken the early game would be; it would boil entirely down to cavalry spam. The only reasons to build units other than Great War Bombers once Flight is discovered are: 1. Great War Bombers can't capture cities and 2. You may need some fighters to counter your opponents' fighters/great war bombers. There are a few possible solutions I can think of. One that doesn't involve changing the tech tree at all is to simply remove great war bombers from the game or nerf them significantly. As it stands, it only takes 3-4 bombing runs to destroy any other period unit, which is ridiculous from both a gameplay perspective (better pick up flight first before ANY other modern tech or suffer the wrath of the bombers, and good effing luck if you're a bit behind in tech) and also from a realism perspective (imagine how different World War 1 would have been if a minimal investment in bombers meant the utter destruction of entire battle lines). Another other solution is to move Combustion SIGNIFICANTLY earlier in the tech tree so at least coastal cities and navies can protect themselves from the horrors of bombers; or to give Machine Guns a low interception chance and move them up before flight (especially considering that Machine Guns should be the overwhelmingly dominant force of WWI from a realism perspective); or to just swap Ballistics and Flight on the tech tree. This exact problem exists with a number of units coming significantly before their counters, but none are so game-changing as bombers coming before any form of anti-bomber measure. I.E.: Submarines before Destroyers Artillery LONG before Landships Landships before Anti-Tank Guns Also, what's up with marines? They seem bizarrely situational. I kind of wish they were part of a tech line coming from Scouts but I guess that's another thread entirely.