Battle of Dienbienphu, Jules Roy, published by Faber & Faber 1963. (Translated from the French).
Many thanks for the recommendation, I've put it on my wants list.
More shocking to me than DBP was the annihilation of two 10,000 strong French columns by the Viet Minh - shades of the disappearance of three Legions and auxiliaries in the Teutoburger Wald.
Try: The Quicksand War - Prelude to Vietnam. Lucien Bodard. Again Faber but published in 1967, even though it covers the period from the end of WWII up to 1950. Rivetting reading. One "money quote", describing Gen Chanson:
Most of his brother generals were quite happy to wage a traditional kind of war; but for his part he had a notion - a rare one among career soldiers - that the primary function of an army was to beat the enemy.
You rarely get this quality of writing in contemporary books.