I read about that service somewhere, they basically cut the boat in half to replace the engines and then welded it back together.
> Rossi called the re-delivery an important milestone for Argentina, as the state had lost its ability to repair submarines following the previous Domecq Garcia shipyards being disbanded.[1]
Distinct lack of details; though the article says crew of 37 when every current article about it missing states 44.
edit: The lack of maintenance facilities is worrying, though it sounds like the overhaul has created a grannies broom; there's not much of the original sub left.
[1] http://en.mercopress.com/2014/06/19/argentine-navy-receives-...
Linked from wikipedia: https://en.wikipedia.org/wiki/ARA_San_Juan#cite_note-5
I've heard of Theseus's Ship, and grandfather's axe - granny's broom is a new one to me.
A few of my software products have gone through multiple frameworks and rewrites, but from the user's point of view they appear to have remained one evolving entity. My phone/personal-digital-assistant also has kept its name for 21 years, but has gone through a series of reincarnations.
It's not that unusual in submarine refits to cut the boat in half and slot in an entire new section!