A sight used to guide the "bouncing bomb" that changed the course of World War Two has been put up for sale.
Towcester auctioneers J P Humbert is offering the Dambusters wooden "Dann" bomb sight for sale for an estimated £20,000 to £25,000.
It was used during the British bombing raid on the Mohne dam in Germany on 17 May 1943.
The sight is one of five pieces of Dambusters memorabilia being auctioned off.
The Dambusters of the 617 Squadron flew from RAF Scampton in Lincolnshire.
The "Dann" bomb sight was designed by Wing Cdr C L Dann and was used by bomb aimer Pilot Officer John Fort on board the AJ-J, the fifth aircraft to attack the dam, piloted by Flt Lt David Maltby.
It was the 'bouncing bomb' guided by this sight which breached the Mohne dam and flooded the western Ruhr region.
It was passed to David Maltby's father, Ettrick, after the raid and placed in the museum of prep school Hydneye House, East Sussex, which he owned and ran.
When the school was sold in the mid-1950s it was passed on to the new head master and eventually to the current owner, a former pupil.
Humberts is also offering the map light and parallelogram used by Sgt Vivian Nicholson, Matlby's navigator on the same aircraft, as well as four of the marbles used by Sir Barnes Wallis to design the 'bouncing bomb'.
A leather collar box which belonged to Wing Cdr Guy Gibson, the commanding officer for the mission, is the fifth item on offer.
Auctioneer Jonathan Humbert said the items were the "most spine-tingling and historical" he has offered for sale.
He said they were "synonymous with heroism of the highest order".
The International Militaria Auction will take place on 20 January.