The first aeroplanes available proved to be unequal to the task, because of the inadequacy of their lifting power. The atmosphere in the tropics is of a totally different buoyancy from that in colder latitudes, and a machine whose engines enable it to mount quite easily to a height of 4,000 or 5,000 feet in Northern Europe, cannot, in Central Africa, rise more than a few hundred feet from the ground. New types of machines, therefore, had to be sent, and these had to be tested and got ready for work. For many weeks then, before the actual attack was undertaken, we must picture to ourselves the Island of Mafia, hitherto unoccupied and indeed untouched by Europeans, in the process of conversion into an effective base for some highly complicated combined operations of aircraft and sea force. The virgin forest had to be cleared away and the ground levelled for an aerodrome. The flying men had to study and master machines of a type of which they had no previous experience. The monitors had to have their guns tested and their structural arrangement altered and strengthened to fit them for their new undertaking. And indeed preparing the monitors was a serious matter. The whole delta of the Rufigi is covered with forest and thick bush--nowhere are the trees less than sixty feet high, and in places they rise to nearly three times this height. To engage the _Koenigsberg_ with any prospect of success, five, six, or seven miles of one of the river branches would certainly have to be traversed. There was, it is true, a choice of three mouths by which these vessels might proceed. But it would be almost certain that the different mouths would be protected by artillery, machine guns, and rifles, and highly probable that one or all of them would be mined. The thick bush would make it impossible for the monitors to engage any hidden opponents with sufficient success to silence their fire. And obviously any portion of the bank might conceal, not only field guns and riflemen, but stations from which torpedoes could be released against them. It was imperative therefore, to protect the monitors from such gun fire as might be encountered, and to take every step possible to preserve their buoyancy if a mine or torpedo was encountered.