Surprisingly to her captors, the ship was armed with 26 × 24-pounder long guns, a main armament that was relatively uncommon for frigates in the 18th century.

During the long war with France, the standard British frigate was of about 1,000 tons and armed with a main battery of only 18-pounders, no match for the big US ships.

They differed from the prototype by being constructed of "fir" (actually, pitch pine) rather than oak, and mounted an extra (fourteenth) pair of 24-pounder guns on the upper deck forward.

All would be reclassified as 50-gun fourth-rate frigates in February 1817; however, the use of softwood in their construction was such that they were only intended for a short lifetime, and indeed all five were taken to pieces after a few years' service.

The first pair were originally ordered on 4 May 1812 as Tagus and Eridanus of the 18-pounder armed Leda class, but were renamed on 7 January 1813 as Severn and Liffey.