Complex sentence: Although raised, in part, to defend against invasion, the yeomanry were only once called upon to do so when, in 1797, William Tate landed at the head of the Légion Noire at Fishguard in Wales.
Split into simpler sentences: Although raised, in part, to defend against invasion, the yeomanry were only once called upon to do so. In 1797, William Tate landed at the head of the Légion Noire at Fishguard in Wales.