A Security Officer on a military base needs to encrypt several smart phones that will be going into the field. Which of the following encryption solutions should be deployed in this situation?

Elliptic curve cryptography (ECC) is a public-key method primarily used for key exchange, digital signatures, or secure key generation, not for the bulk symmetric encryption of data on a smartphone.

A one-time pad is theoretically unbreakable but practically impossible to manage for encrypting multiple smartphones due to the insurmountable challenges of generating, distributing, and securely managing unique, truly random keys equal in length to the plaintext for each device.

3DES (Triple DES) is an older symmetric encryption algorithm that is significantly slower and less secure than AES, having been superseded due to its vulnerability to meet-in-the-middle attacks and its smaller effective key size.

AES-256 (Advanced Encryption Standard with a 256-bit key) is a modern, strong, and widely adopted symmetric-key encryption algorithm, designated by NIST as a standard for encrypting sensitive government data. It provides excellent security, performance, and hardware support for data at rest, making it the most appropriate choice for robust smartphone encryption in a military context.