I read Elford's Devil's Guard when I was about 14 (that was in the 1970s) and was dubious about how true it was, so I was attracted to this title to see whether it really did tell the real story of the Foreign Legion in Vietnam. Far from it. The narrator claims to be a former Sturmbannfuhrer of the Das Reich division and that division's most decorated officer. The decorations he claims are similar to those of Das Reich's most decorated officer, who was a Sturmbannfuhrer (and who was responsible for the Oradour-sur-Glane massacre) but he was killed in action in October 1944. The narrator's ex-Waffen SS comrades in the Foreign Legion are former members of the Leibstandarte, Das Reich and Totenkopf divisions - why only those three? They are said to be experienced in anti-Partisan warfare but if you wanted Waffen SS men with extensive anti-Partisan experience, you would get them from the Prinz Eugen or Florian Geyer divisions - one suspects that the author has never heard of them. One of the the narrator's squad has lost an eye and sports a black eye-patch - would the Legion really have accepted a one-eyed recruit in 1946 or '47?
The book has none of the flavour of true-life war stories (I'm thinking of Chickenhawk, A Rumor of War, Bravo Two Zero, Skorzeny's memoirs), the narrator tells us none of his back-story, we don't know where he was born, how old he is, when he joined the SS, when he joined the Legion, how he came to be a senior sergeant; it reads more like a Hollywood film script: it opens with a French unit facing massacre being rescued by a passing Foreign Legion patrol, on their way back to Hanoi they come across a village whose population has been massacred by the Viet Minh, further on they are ambushed and when they finally reach their barracks, it comes under attack: all in one afternoon! There is more action the following day but a few days later our heroes are able to train for their special mission for three weeks without interruption (it isn't obvious why they would have needed training, have they accomplished all their recent exploits without being fighting-fit?). The explanations of the historical background (Einsatzgruppen, the Luger pistol, Stalingrad, Operation Citadel) seem to have been lifted from an encyclopedia and there is nothing to suggest that the author has been closer to Vietnam than the South-East Asia page of his atlas.
So if this is not fact, how is it as fiction? Not very good: the narrator should be played by Randolph Scott; although a former SS man, he has never killed a civilian, is not an anti-semite, and wasn't a Nazi (why did he join the SS?). All the characters in the book are one-dimensional, everything goes according to plan, they meet no problem they cannot handle, no one gets wounded; when one of them is killed it means nothing to us because he was never more than a name and it seems to have no impact on his comrades either. There's an improbable love-interest in the form of a 28-year-old French doctor who they come across during their secret mission - we are told that she was born in 1924 so we can calculate that the action is supposed to take place in 1952 - she and the narrator first make love in the jungle while hiding from searching Viet Minh forces: yeah, right.
The original Devil's Guard was probably invented, Devil's Guard - The Real Story certainly was.