The 5-Man Army (1969)

Set during the Mexican Revolution, a man known only as "The Dutchman" has a plan, and brings in four of his old acquaintences, including an old army buddy and a silent Japanese swordsman, to help him out by promising a $1000 reward if it succeeds. The plan turns out to be a fool's mission: rob a train carrying $500,000 in gold that's guarded by dozens of heavily armed soldiers and passes through a steady stream of military checkpoints. Naturally, his friends agree to go along with the scheme.