Gálvez had originally planned to march from New Orleans on August 20.

However, a hurricane sweeps over New Orleans on August 18, sinking most of his fleet and destroying provisions.

Undeterred, Gálvez rallies the support of the colony and on August 27 set outs by land toward Baton Rouge, using as an explanation for the movement the need to defend Spanish Louisiana from an expected British attack.

He leads a force that consists of five hundred and twenty regulars, of whom about two-thirds are recent recruits, sixty militiamen, eighty free blacks and mixed race people, and ten American volunteers headed by Oliver Pollock.

The force grows by another six hundred men, including natives and Acadians, as they march upriver.

The force at its peak numbers over fourteen hundred, but this number is reduced due to the hardships of the march by several hundred before they reach Fort Bute.