Complex sentence: Montagu was the eldest son of the 9th Earl of Sandwich, was educated at Eton and Trinity College, Cambridge and in 1926 he joined the 5th (Huntingdonshire) Batallion of The Northamptonshire Regiment as a Lieutenant.
Split into simpler sentences: Montagu was the eldest son of the 9th Earl of Sandwich, was educated at Eton and Trinity College, Cambridge. In 1926, he joined the 5th (Huntingdonshire) Batallion of The Northamptonshire Regiment as a Lieutenant.