Complex sentence: Prior to the Colonial Police under Pemberton, the Victoria Voltigeurs existed as an armed, uniformed militia that served all Vancouver Island on an "as and when needed" basis.
Split into simpler sentences: Prior to the Colonial Police under Pemberton, policing on Vancouver Island was conducted by the Victoria Voltigeurs. The Voltigeurs existed as an armed, uniformed militia that served all Vancouver Island on an "as and when needed" basis.