Aud was the cover name

Pseudonym

A pseudonym is a name that a person assumes for a particular purpose and that differs from his or her original orthonym...

 of a German ship, Libau, that carried arms to Ireland as part of the preparation for the Easter Rising

Easter Rising

The Easter Rising was an insurrection staged in Ireland during Easter Week, 1916. The Rising was mounted by Irish republicans with the aims of ending British rule in Ireland and establishing the Irish Republic at a time when the British Empire was heavily engaged in the First World War...

 in Ireland in 1916.
Masquerading as the Aud, an existing Norwegian vessel of similar appearance, the SMS Libau (formerly the Castro) set sail from the Baltic port of Lübeck

Lübeck

The Hanseatic City of Lübeck is the second-largest city in Schleswig-Holstein, in northern Germany, and one of the major ports of Germany. It was for several centuries the "capital" of the Hanseatic League and, because of its Brick Gothic architectural heritage, is listed by UNESCO as a World...

 on April 9, 1916, under the Command of Karl Spindler, and his crew of 22 men, all of whom were volunteers.