No, taking out the transformers, which can have lead times of three to five years, will result in the most long-term damage. You can't just pull one out of storage and drop it into place.

How about use drone submarines to cut optic fibre undersea cables?

Ukraine has proven otherwise. A lot of European countries pulled them out of storage and gave to Ukraine. Of course there will be a limit to this if you destroy enough of them.

Europe scraped together some transformers they'd been holding in reserve as spares and hoped they wouldn't need them themselves at some point, but once they were gone, they were gone. https://www.bloomberg.com/features/2025-bottlenecks-transfor...