1 shaving is enough to do catastrophic damage. Bigger engines don't have bigger clearances ;)

So why did they use kilograms if grams would have worked fine?

Higher probability of success. With 1 shaving it could make it to an oil filter without lodging anywhere critical (like in a main bearing oil gallery or something). With a huge number of them the likelihood of clogging oil galleries and overwhelming the filtration system is very high. Also, the secondary point of the sabotage is to be detected. Even if the engine doesn't grenade itself through the hull of the ship, when they discover widespread contamination in the lubricating oil they'll have to remove and completely disassemble every single part of the engine and lubrication system. Effectively a total rebuild. So "no permanent damage" is really a very rose colored way to frame it. The cost is roughly the same.

EDIT: a super devious way to do it would be with very small magnetized filings. It would be incredibly difficult to rid the engine of those, even completely disassembled.

Nailed it.

This was a huge security screw up, you have to draw your security barrier and they left this huge asset on the wrong side of it. If only the followed Gauss's Law.

The ship hasn't been put into service yet. It's still with the shipbuilders, where I suspect that security is much weaker than on a navy base.

It's a security screwup that a ship was scheduled to be in service, but now that date might be delayed. The entire point of the boat is security. They didn't secure the thing that provides even more security.

It would have been a much bigger security screwup if it was actively in service.

> a super devious way to do it would be with very small magnetized filings. It would be incredibly difficult to rid the engine of those, even completely disassembled.

Just heat it.