They shared, among other things, a practical intelligence — the ability to see through complex situations to their operational essentials — that expressed itself differently in each man but that made them effective collaborators.

Grant’s military genius was largely operational and strategic: he understood logistics, he understood what was required to move large bodies of men and supplies, and he had the psychological capacity to absorb setbacks without being paralyzed by them.

Parker’s strengths were organizational and communicative: he was precise, systematic, and capable of translating complex deliberations into clear written records.

When Grant needed someone to serve as military secretary — the officer responsible for managing the communications of a major command — Parker was a natural choice based on actual qualifications rather than sentiment.

The role required exactly the skills Parker had demonstrated over his entire career: precision, literacy, the ability to work quickly under pressure, and the organizational discipline to maintain clear records in chaotic conditions.