Complex sentence: Perhaps the British were prepared to take advantage of a German invasion when Irish Troops would be fending off attack by retaking the Treaty ports, or if they felt de Valera was slow in asking for intervention.
Split into simpler sentences: Perhaps the British were prepared to take advantage of a German invasion when Irish troops would be fending off attack by retaking the Treaty ports. They may also have been prepared to act if they felt de Valera was slow in asking for intervention.