Will Portsmouth harbour look strangely bare without this 7000-tonne feature?
The 7,000-tonne destroyer is to be refitted to allow her to continue her role an accommodation and training ship for the navy, cadet forces and youth organisations until 2025.
She is expected to be absent from the moorings off Whale Island for up to six months, with an expected return date of early to mid March 2011.
Since 1993 the depth around the moorings is thought to have reduced by up to 2 metres, so the opportunity will be taken to carry out dredging work.
Bristol was the last surface warship designed for the Royal Navy to be powered by steam, and had a unique funnel layout with two side-by-side funnels aft of a single larger funnel.
She remains in commission, has an RN Commanding Officer, and provides 460 berths for the fourteen thousand young people who pass through her every year.