An animal "Victoria Cross" awarded to a dog for bravery during World War II is expected to fetch up to £30,000.
Collie Sheila received the PDSA Dickin Medal for helping to rescue US airmen from a plane which crashed on the way back from an aborted bombing raid.
Sheila and master John Dagg battled blizzards to reach the crash site in Northumberland and find the four men. By the time they reached the crash scene, Sheila had found pilot Lt George Kyle, and Sgts Howard Delaney, George Smith and Joel Berly.
Mr Dagg administered first aid and led the party down the mountain as the B17's bombs exploded. Three other crew also escaped, but two others died.
Mr Dagg was awarded the British Empire Medal and both medals will be sold on Tuesday at Morton and Eden in London.
Sheila became the first civilian animal to receive the PDSA (People's Dispensary for Sick Animals) Dickin Medal the next year.
Mr Dagg later sent one of the collie's puppies to the US-based family of Sgt Frank Turner, who did not survive the crash. The PDSA Dickin Medal was instituted in 1943. Between then and 1949 it was awarded to 32 pigeons, 18 dogs, three horses and a cat called Simon.