Legge was born at
Cullenswood,
Van Diemen's Land. His father, Robert Vincent Legge had moved from Ireland to Van Diemen's Land in 1827 along with his sisters and was married to Eliza Graves (née de Lapenotierre). He was granted 1200 acres (486 ha) which he named "Cullenswood" after his home in Ireland. William was sent to study at
Bath after which he continued studies in France and Germany, picking up several languages before joining the
Royal Military Academy, Woolwich. In 1862 he was commissioned into the
Royal Artillery, serving first in
Bath, England, and then in
Melbourne for several years. From Melbourne his battery was transferred to
Colombo,
Ceylon, where he was stationed 1869–1877. He then took a staff appointment at
Aberystwith,
Cardiganshire, for five years. Subsequently, he moved back to Tasmania. He was involved in the defence of the River Derwent and setting up batteries to defend Hobart with new guns. With a recommendation from Sir
Peter Scratchley he served for eleven years as Commandant of the
Tasmanian Defence Forces, retiring as
Lieutenant-Colonel from the Imperial service in 1883. He trained Tasmanian forces for the
Second Boer War and organised in 1900, the reception for the Duke of Cornwall. He continued in service until 1904, when the forces were taken over by the Commonwealth. Legge had early shown great interest in the defences of the River Derwent, and for this and a recommendation by he was offered the command of the forces in Tasmania. He took up his new command on 6 December 1883, retiring from the imperial service with the rank of lieutenant-colonel. In April–May Legge had completed the torpedo course on H.M.S. Vernon at Portsmouth, and with advice from Scratchley and General Hardinge Steward ordered the new breech-loading guns for the colony from the Elswick Works at Newcastle upon Tyne. During his command the forces were entirely reorganised and the batteries defending Hobart were completed and armed with several of the latest types of guns, but many of his other recommendations went unheeded. He was twice re-engaged before his appointment ended in June 1890 through government retrenchment. When Colonel A. T. Cox retired in 1898 the command was again offered to Legge. He trained Tasmanian contingents for the Boer war and was in charge of the reception of the Duke of Cornwall in 1900, and held his post until the forces were officially taken over by the Commonwealth in 1904. ==Scientific career==