Is SHA-256 military grade?

Yes- SHA-256 is integrity and not secrecy military grade encryption. NSA developed the whole Sha-2 family and the SHA-256 is approved by the NSA to secure the Secret-level digital signatures and blockchain ledgers. Although it has no encryption functions of its own, any military grade encryption mechanism (including AES-256 disk in a submarine) uses SHA-256 to ensure that no foe intercepted even a single bit on its way.