Porcupine was rated a 24-gun ship and the original plan was that she would mount that number of long 9-pounders on her main deck plus two 6-pounder guns on her forecastle. She also carried ten 24-pounder carronades on her quarter-deck and forecastle. By the time that Captain the Honorable Henry Duncan commissioned her in March 1807, the Admiralty had added two brass howitzers to her armament, while exchanging her 9-pounders for 32-pounder carronades. Her complement was increased by twenty to 175 officers, men and boys.