As Attorney General, it was his responsibility to lead the prosecution for the Crown in major cases such as the trial in 1916 of the Irish nationalist Sir Roger Casement for treason. Sir Roger had been captured after landing from a "Kaiserliche Marine" U-boat on Banna Strand in Tralee Bay in north County Kerry, south-west Ireland, just a few days before the Easter Rising in late April 1916. His prosecution of Casement (and Wheeldon in 1917) contributed to Smith's reputation as a spectacular advocate at the time.