Acts 27:43

But the centurion, desiring to save Paul, stayed them from their purpose; and commanded that they who could swim should cast themselves overboard, and get first to land.

Stayed them from their purpose ... Only a command from the centurion was sufficient to do this, and he promptly gave it. The actual danger of prisoners escaping was genuine; and, accordingly, he commanded the soldiers who could swim to go overboard at once, thus getting to land first, and thereby being able to keep sharp watch on all of the prisoners.