A hostile procurement list pairs impressive ships with hidden weaknesses

If you secretly worked for the enemy while buying a late-1930s navy, which apparently good ships would you choose to make the fleet ineffective?

Bismarck-class ships with Italian shells, German destroyers, Japanese light cruisers, and early Soviet submarines.

The proposed purchases look formidable while carrying operational or technical liabilities. Bismarck-class capital ships receive Italian-produced shells, combining a famous design with ammunition-quality risk. German destroyers are selected because they were well built yet poor at the destroyer role, while Japanese light cruisers offer another compromised choice. Early Soviet submarines complete a fleet whose specifications can impress a government even as its fighting qualities are quietly undermined.