Medium-speed diesels trade compactness for flexibility

Could medium-speed diesels replace scarce high-speed engines in a modern frigate?

Yes, especially as generator sets, but they need more hull volume, subdivision, and attention to fuel and lubrication demands.

Medium-speed diesels are technically possible, particularly when they produce electrical power rather than driving shafts directly. The price is space because more or smaller engines have to be distributed through the hull. That changes subdivision, weight, fuel use, and oil requirements. The choice is a procurement tradeoff between a compact specialised plant and a more available, space-hungry alternative.