Shout at the Devil (1976)

Just before World War I, the hard-drinking, sharpshooting, Irish-American Colonel Flynn O'Flynn uses British aristocrat Sebastian Oldsmith to help poach ivory from German-controlled territory in East Africa, putting them at odds with Herman Fleischer, the local German Provincial Commander. When Sebastian is infected with malaria, he is nursed back to health by Flynn's daughter Rosa, and they fall in love and marry. Not long afterwards, Britain declares war on Germany and they are drawn into the conflict, ultimately making a daring attack on the German armored cruiser S.M.S. Blücher as it undergoes repairs in a local estuary.