Russia - threadbanned users in OP

No, but I wouldn't underestimate the ability to repair a bridge if they really want to. I am reminded as to how long it took to repair the Oakland Maze bridge after the fire and collapse (One bridge fell onto another bridge). Initial estimates using normal processes were a month just to clean up the mess, and more months to fix it. By saying "Sod the money, get it fixed now" because of how critical it was to get the bridges running again, the job was completed in less than a month.

I can think of two obvious ones and one less obvious one.

1) Soviet Union, 1940. The Soviets got their asses kicked by Finland in the Winter War. They eventually made it, but it was a wake-up call to the Red Army. They immediately started reforms. By the time the Germans had attacked in 1941, the reforms were well under way, but not yet truly effective. However, the Germans had been lured into thinking the Russians were easy pickings by how badly they had performed the year prior. It wasn't just German error which led to their defeat at Moscow, the Soviets did good too. Reforms continued for the next couple of years, and by the end of the war the Soviets were as competent and dangerous as any military on the planet. This is the example which worries me, as the longer this Ukraine thing goes on, the longer the Russians have to stop being idiots and start properly addressing their failings. I will say that they have been adapting on the tactical level, they aren't all unmotivated idiots at the front line. When this happens at the national level, the Ukrainians will be in trouble a few months after that.

2) US Army, 1940. Starting with an army smaller than that of Romania, with generally poor equipment, not having conducted a major exercise in nearly two decades, and decidedly questionable reserves, within two years was conducting offensive expeditionary warfare on two continents. Even the famous defeat at Kasserine late 1942 demonstrated capability, as the Germans were also defeated in their operation. The US didn't look back after that. How the US managed that is a case study in national mobilisation and military reconfiguration/retraining which I doubt will ever be equalled.

3) US Army, 1980. Coming out of the Vietnam war, the US Army was of low morale and relatively unprofessional and ill-disciplined. Dangerous, yes, but not what you would expect of a superpower. A determined effort to 'professionalize' the Army as it returned to an all-volunteer force combined with an equipment rejuvenation resulted in the most overwhelming army on the planet as demonstrated ten years later.

The Ukrainian turnaround since 2014 has certainly been impressive, but don't overstate it. They are not to the standards of a modern NATO force and it's something of an exponential scale. Going from 'incompetent' to 'adequate' is much easier than going from 'adequate' to 'good', and going from 'good' to 'excellent' is extremely different. I feel like the European observers did in the American civil war, from their perspective they were watching amateurs fight incompetents.