The Dieppe Raid is perhaps the best known and the least known about of all the important actions of the Second World War. The complete facts were never made known to the public, and the scrappy bits and pieces published at the time created a sense of frustration and unease. Sir Winston Churchill wrote ''Military opinion seemed unanimous that until an operation on that scale was undertaken no responsible General would take the responsibility of planning for the main invasion.''Thompson''s book is history, very old-fashioned history, and he has done his utmost to lay down the facts clearly. The brief snatches of dialogue quoted are authentic, usually word for word, but always sticking to the simple sense of what is known to have been said. For example, Sergeant Dubuc, being a French-Canadian, may have cried, ''Sauve qui peut!'' the moment after he had killed the German guard. He certainly said something very like that in French or English.