Afaik governments usually don't insure such mishaps. They have pretty much unlimited funds in comparison with insurers. Subcontractors couldn't insure themselves for these kinds of liabilities. No insurer would go that high in liability. Insuring military apparatus itself, well kind of beats the point. Insuring machines of mass destruction against destruction... On the outliers of 'crazy' insurance that I know are things like (private) sattelites and of course the global nuclear pool.