While wandering around the 4th Squadron's page I came on this piece:

"GarryOwen is also the Regimental March of another famous fighting unit, The Royal Irish Regiment. Organized in 1684 from Irish Pikemen and Musketeers, this regiment has seen service in all parts of the world. For their outstanding valor at the Battle of Namur, they received the title of "The Royal Regiment of Foot of Ireland". The Royal Irish showed noble courage and performed gallant service throughout the Crimean War. On their colors are inscribed "Egypt," "China," "Blenheim," "Ramillies," "Oudenarde," "Malpaquet," "Pegu," "Savastopol," "New Zealand," "Afghanistan, 1879-80," "Egypt, 1882," "Tel-el-Kebir," "Nile, 1884-85," and "South Africa, 1900-02."

One cannot wonder how many of the former members of the Royal Irish Regiment emigrated to the United States and enlisted as troopers of the US Cavalry Units. Could this have been how Custer heard this song?"

To which I'd add, Garry Owen certainly has an ancient military linneage - as old as many items of Irish culture extant and certainly older than the 7th.