Brooke had been instructed not to attack the American positions around Baltimore unless he was certain that there were less than 2,000 men had to withdraw from his positions and returned to the fleet which would set sail for New Orleans.
Unless he was certain that there were less than 2,000 men had to withdraw from his positions. This was what Brooke had been instructed not to attack the American positions around Baltimore. Brooke had been returned to the fleet. This fleet would set sail for New Orleans.