Berlin’s newest trains are also going to be its oldest trains: the subway is currently so short of rolling stock it’s bringing back 3 of the “Doras”, the first of its trains built after World War 2, complete with vintage adverts.
Ironically they’re coming back into service on Berlin’s newest bit of subway, the U55, which was initially planned to provide a transport link for the then newly Berlin-based German government with the rest of the city after unification became a thing in the early 1990s. The U55 line was plagued with a number of delays - for many years no-one wanted to pay for it, then once they did it flooded - but was finally opened in 2009 as a mile-long stub of a line that’s not properly connected to anything else: London readers can basically think of it as Berlin’s Waterloo and City line.
There is a plan to make it a bit more useful by extending it and connecting it up to the U5 (which was always the plan, before they ran out of money the first time around), but until then Berlin isn’t wasting any fancy new trains on it, so they’re making a feature of running some of the network’s oldest stock - the D series, originally introduced in 1957. The trains, which will be refurbished up to modern standards, are among the last of their kind still kept in Germany - most of them were flogged off to North Korea in the 1990s. When the link with the U5 is completed, in 2020, the last Doras will finally be allowed to rest.
This will make the nearly 60-year-old trains among the oldest to run on any European subway service - beating the 1960s trains that ran on the London Underground’s Metropolitan Line until 2012 (the last tube trains to have luggage racks and umbrella hooks!). They’ll still be some distance short of the world record holder - Buenos Aires’s 100-year-old La Brugeoise rolling stock, which was finally retired in 2013.
The record in Europe is the original Glasgow Subway stock, which lasted from the opening of the system in 1896 until 1977, although the ex-London Underground stock living out its “gentle retirement” on the Isle of Wight’s railways is getting close, if you count subway trains that aren't really subway trains anymore.