Tarzan the Untamed (Book #7) by Edgar Rice Burroughs ISBN 13: 9780345241665

From the book:Hauptmann Fritz Schneider trudged wearily through the somber aisles of the dark forest. Sweat rolled down his bullet head and stood upon his heavy jowls and bull neck. His lieutenant marched beside him while Underlieutenant von Goss brought up the rear, following with a handful of askaris the tired and all but exhausted porters whom the black soldiers, following the example of their white officer, encouraged with the sharp points of bayonets and the metal-shod butts of rifles. There were no porters within reach of Hauptmann Schneider so he vented his Prussian spleen upon the askaris nearest at hand, yet with greater circumspection since these men bore loaded rifles - and the three white men were alone with them in the heart of Africa.