Upon their arrival, they find that the fort has been ravaged by Tuareg attacks and American Beau Graves (Guy Stockwell) is the only survivor.
Beau's column had been serving under Lieutenant De Ruse (Leslie Nielsen) and Sergeant Major Dagineau (Telly Savalas), the latter of whom is notorious for his harsh treatment of the men under his command.
He is especially sadistic towards Beau's class of recruits, hoping this will get them to reveal to him which of the men is the author of an anonymous letter Dagineau has received threatening his life.
To ferret out more information, Dagineau uses the services of the slimy toady Boldini (who has reenlisted in the Legion), promoting him to Corporal as reward for his spying on the men.
But, as he later relates to his younger brother John (Doug McClure), who has finally managed to track him down with the same news, he deems it unfair to ask her to wait for him, as he is now committed to a five-year enlistment, with no guarantee he'll survive it.
Over brandy, De Ruse informs Beau of Dagineau's background as a former St. Cyr educated officer who was broken to the ranks when his entire command deserted from his leadership.
With Dagineau back in charge, the brutality returns and it isn't long before the legionnaires mutiny, with everyone except Beau and John set upon executing the sergeant.
Despite their personal hatred for Dagineau, no one doubts his excellence as a battle commander, so Beau convinces the men to release him that he may lead them in defending the fort.
"[5] As a publicity gimmick, Seltzer tried to track down a number of Foreign Legion veterans, asking to see if they were interested in appearing in the film.
[8] The film was the last credited work of Donald Robert Overall Hatswell (born July 3, 1898 in Norwood, Surrey, died: June 29, 1976).
Hatswell was a former World War I Royal Navy Officer whose collection of over 720,000 picture postcards of uniforms and medals led him to be a Hollywood movie technical advisor[9][10] Joseph Kane acted as the film's second unit director.