[Sidenote:  Lakes and mountains a frontier for defense.]

I have referred to these lakes and to the great mountain-chain along the lakes because they formed the western boundary of German East Africa, and from the point of view of defense made a magnificent frontier so strong that the Belgian forces moving from the Congo found it impossible to invade the enemy territory from the west, and had to be moved in large part northeast before they could strike south.  Once there, with their usual dash they did their work remarkably well.

[Sidenote:  Seaplanes attack German vessels in the lakes.]

As soon as this northern column had reached Kigali, the capital of the lofty Ruanda Province, the German forces fell back from the neighborhood of Lake Kivu, and the remainder of the Belgian army was able to advance from the west across the mountain barrier.  Simultaneously, and in cooerdination with their advance, strong British columns were moving southward to the west of Victoria Nyanza.  As soon as we had reached the southern shores of the lake, a new concerted forward movement by the British and Belgian columns was begun both from Victoria Nyanza and from Tanganyika, where in the meantime the German armed vessels on the lake had been bombed and destroyed by seaplanes, and Ujiji on the eastern shore had been occupied.  This movement did not stop until Tabora, with the central railway, was occupied early in September, 1916.

[Sidenote:  General Northey’s advance across the mountain.]

At the same time a great movement was made in the south by General Northey, who advanced from the line between Lakes Tanganyika and Nyasa across the mountains flanking the great plateau on the west.  This is a very mountainous region; but he got over the mountains, and moving north, took Bismarckburg, Neu Langenburg, and afterward Iringa, where our main forces joined hands with his.  These advances, all carried out with great skill and energy against very great physical difficulties, were subsidiary to the principal attack, which was being executed from the north-east, in the neighborhood of Kilimanjaro.

[Sidenote:  The River Rovuma a strategic line.]

[Sidenote:  Pursuit of enemy across Rovuma is difficult.]

The southern boundary between German East Africa and Portuguese East Africa was formed by the River Rovuma, which, coming from the high plateau and the mountains to the east of Nyasa, is one of the large African rivers.  Except in its highest reaches near Lake Nyasa it is not fordable, and makes an admirable strategic line.  However, as Portugal came into the war after most of the German colony had already been occupied by us, this river acquired strategic importance only toward the end of the campaign, and then in a sense adverse to us, as General Van Deventer has found to his cost.  After the remnants of the German native forces had been driven across the Rovuma at the beginning of December, 1917, our forces found the swift pursuit across the river a difficult task.  We are, however, now operating against the roving bands into which the enemy force has split, and if ever they try to break back to their occupied colony, they will find the line of the Rovuma a very serious barrier.