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She could easily have been in place of the entrance to Charleston harbor to participate in that operation.
If you read further into his accounts of the situation, he said they intended to rely on the small boats carried by the Powhatan, and that this wouldn't have worked anyways because none of the Powhatan's boats were usable. They were all in a terrible state of disrepair and would sink if put into the water.
He is justifying what he did. He is rationalizing, or perhaps seeking to divert attention from what he was ordered to do. Again, he never released a copy of Lincoln's secret orders to him.
Where does Porter he discuss receiving secret orders from Lincoln. Other than the three orders he drafted for Lincoln’s signature.