 One of the first tasks for the new army was to suppress the smuggling of slaves from <unk> on the mainland to the island of Pemba , north of Zanzibar . The troops completed this mission , capturing several <unk> and hindering the trade . Mathews retired from the Royal Navy in June 1881 and was appointed Brigadier @-@ General of Zanzibar . In 1880 , the Sultan dispatched a military force under Mathews to bring his unruly African mainland territories under control . Mathews ' expedition was initially intended to reach <unk> but his men refused to march inland and , when made to do so , deserted in large numbers . The expedition ended instead at <unk> where a 60 @-@ man garrison was established . This had been reduced to a mere handful of men by the mid @-@ 1880s but the expedition proved that the Sultan was serious about maintaining control of all of his possessions . Mathews ' men were also involved in several expeditions to halt the land @-@ based slave trade which had developed once the seas became too heavily <unk> for the traders . 
