 He later served under the Mahdi's successor Abdallahi ibn Muhammad (known as the Khalifa), who launched a series of military operations in subsequent years.Osman took command of a Mahdist force invading Ethiopia in 1885, but was defeated by Ethiopian general Ras Alula at the Battle of Kufit on 23 September.In December, 1888, he fought at the Battle of Suakin, attempting to capture the local Water Forts.