During this period, Herbert continued to compose operettas, producing two of his most successful works, "Naughty Marietta" (1910) and "Sweethearts" (1913). He also became progressively more involved with Irish-American organizations: in 1908 he joined the Friendly Sons of St. Patrick (becoming president in 1916), the oldest Irish association in New York, and in 1911 he became a member of the American Irish Historical Society. In early 1916, he became the founding president of the Friends of Irish Freedom and became active in the cause of Irish nationalism. Another operetta, "Eileen" (1917, originally entitled "Hearts of Erin"), was the fulfillment of Herbert's desire to compose an Irish-themed operetta and a tribute to his grandfather's novel "Rory O'More". The piece is set during the Irish Rebellion of 1798 and contains a rich score; it debuted in time to mark the first anniversary of the 1916 Easter Rising in Ireland. This was the end of Herbert's greatest period of producing full scores for operettas. In late 1916 Herbert also orchestrated "Soldiers of Erin", an English language version of what would later be adopted as the Irish national anthem; it was widely performed in the US from early 1917.