I'm from Hungary and my grandfather was a senior engineer in a foundry and in a factory producing agricultural wehicles. My father told me that my grandfather had documents which were like plans to convert the production lines in 24 hours to make war supplies in case of a war breaks out. I've heard theories like this before (the most widespread is that the cigarette factories could make bullets) but I always considered them urban legends. Is there any truth about this? Could my grandfather have that kind of documents?
Christopher Lennert's "Tankograd" relates how the factories of Cheliabinsk had plans established pre-WWII to convert them to wartime production. So for example the tractor factor was to switch to production of heavy tanks. To do this plans were drawn up and some equipment (and IIRC some material) was supposed to be held at the complex, and the plans and level of preparation was reviewed from time to time.
One of the things Lennert notes is that these preparations were often found wanting - things like the plans not being realistic or the reserved material not being there/ready. Also in practice converting Cheliabinsk into 'tankograd' ended up requiring (or at least benefitting) the transfer of labour and skilled engineers from Leningrad. That being said that anyone was checking up on those plans etc. in the pre-war period suggests they were being taken reasonably seriously.
So could a factory that built heavy machinery in the Eastern Bloc (I'm guessing this is post WWII) have had a similar war plan? Probably. I would be semi-surprised if a tractor factory could really build... say a T-62, from scratch without inputs from another production line elsewhere. Things like the anti-radiation lining in the armour seems a little too item specific. Then again I don't know if industry in Hungary had the same approach as the Soviet one e.g. building the whole unit at one complex, instead of certain parts being built by specialised industries then shipped for assembly.
In 24 hours? That seems very improbable. The time needed to re-arrange the equipment, get the relevant inputs etc. would take more than a day no matter how well planned the change over would be. All it would take is for one thing to go wrong somewhere (and that includes stuff being done too early ironically), and the timetable would be thrown out. Maybe the equivilent of 'phase 1' was supposed to be done in 24 hours, with further roll out (e.g. converting more production lines) after that.