[Vespers War]

It's also worth noting that Lend-Lease locomotive supplies were a major factor in the USSR being able to switch its locomotive factories to tank production. The USSR built 354 locomotives in 1941. For the entire rest of the war, they produced 92. Lend-Lease delivered 1,911 locomotives to the USSR. Without those, their needs for rail logistics would have required them to keep locomotive factories building locomotives instead of tanks.

On the modern end of things, I think the return of trench warfare has been mildly surprising but makes sense. Both sides have large forces with significant differences in level of training within their forces, so lesser-trained soldiers can hold ground within fortifications to discourage opportunistic attempts to break through them, requiring more significant resource investment that is more likely to be spotted in advance. A TDF or a group of mobiks still might not be able to completely stop a determined attack on their own, but they can slow it down enough for units with more training and equipment to reinforce the position.

I think the US has done better with anticipating drones than Russia, but there are still some things that were missed. The low-end attack drones, like TB2 or Shahed or Orlan, are things that were mostly ignored on the US side in favor of more capable systems. But those drones have an additional effect in that a lot of the air-defense systems capable of taking them down use missiles that are more expensive than the drone. If it costs more to destroy a drone than to build a drone, over time the economics favor the cheap drone. I think the eventual counter to this will be smarter cannon rounds for air defense artillery, like some of the 30, 35, and 40mm rounds that have started entering service but (AFAIK) have not been provided to Ukraine. I also think we may see more SHORAD platforms that have a combined gun and missile armament like Tunguska and Pantsir (although hopefully more effective than Pantsir, which seems to have performed atrociously in this conflict). Something mounting a 30mm or 35mm autocannon with modern flak rounds and a 4 or 6 of whatever IR-guided missile replaces Stinger would be about what I'm thinking we may see around the end of the decade. SHORAD has been oriented towards taking down fast jets for the last few decades, and will need something extra to handle cheap, slow drones that cost less than a missile.