A Spanish official told the Associated Press at the time that someone had put a decimal point in the wrong place, and “nobody paid attention to review the calculations”.
This article was amended on 19 July 2018 because an earlier version said in the next few days the Spanish government would approve raising the total additional cost of the new submarine by €1.7m. This has been corrected to €17m.
It's like the Spinach Submarine:
https://www.theguardian.com/world/2018/jul/19/too-long-to-fit-launch-of-new-spanish-sub-runs-aground