Plot hole: Alain joins the Legion, goes through extensive training and eventually gets his photograph taken. That's how Galgani recognises him and sends two men to kill him. They arrive with a platoon at the fort just after Alain, Mackintosh and Luther. The photograph would have taken a while to get back to France and then the two men would have to go through the same training. So how do they both end up in the same fortress after they joined the legion long after Alain?
Plot hole: Normally, one's first reaction upon grabbing hold of a smoking explosive satchel would be to fling it away quickly, correct? Why oh why then did the Legionnaire officer grab it and run away with it in his hand, causing it to blow him (and all the ammunition) to bits moments later? A pretty senseless act for an experienced commander, if you ask me.
Plot hole: When the Arab horsemen swarm into the Legionnaire fortress during the final assault at the end of the movie, the Legionnaires all crowd at the smoke-filled gate entrance and fire blindly into the haze, hoping to hit something. That's dumb! Couldn't they have pulled back and lain in wait, picking off the Arabs one by one as they rode through the gateway? It's basic military tactics!
Plot hole: As the ambush at the waterhole concludes and the Arabs withdraw (having captured the Legionnaires' supplies), the Arab leader Abd El-Krim rides up in open view on a high rock to survey the shattered Legionnaire forces. Heh, why didn't anyone think of getting a good, clean shot at him then?