The "Birkenhead" was never commissioned as a frigate, as two factors came into play while she was still under construction, that resulted in her being converted into a troopship. Firstly, the Royal Navy's warships were switched from paddle wheels to more efficient propeller propulsion, following an experiment organised by the Admiralty in 1845 in which the benefits of the propeller over the paddle wheel were dramatically demonstrated. Secondly, the Admiralty had doubts about the effects of cannon shot against iron hulls – in a number of trials carried out at Royal Arsenal in 1845, at lower velocities shot made a jagged hole that was hard to plug. On 15 September 1847, "Birkenhead" ran down and sank the brig "Oratio" in the English Channel off The Lizard, Cornwall. The owners of the brig sued for their loss in the Admiralty Court. "Birkenhead" was found to be to blame as she had no look-out posted, being nineteen short in her crew.