A businessman and friend of 93-year-old Robert Noble has offered a Â£5,000 reward for information in a bid to help police trace the "despicable" thieves.
Decorated World War Two veteran Mr Noble kept cash, bank cards and war memorabilia including demob papers along with his late wife Sally's wedding and engagement rings in an 18in x 18in green metal box at his home on Church Lane, Garforth.
Other personal items belonging to Sally Noble, who died aged 84 in 2010, were also in the box.
Two men posing as water board officials conned their way into visually impaired Mr Noble's home before one stole the box, which also contained Â£3,000 cash.
It is believed the burglars struck between 1pm and 4pm on Tuesday.
Mr Noble's son Richard, 59, said his father was desperate to serve his country and lied about his age to sign up in the army aged 17.
He served as a bren gunner with Black Watch battalion and saw active service in North Africa, Greece and Sicily and was involved in the Battle of Monte Cassino in Italy in 1944.
After the war the father-of-four worked as an engineer for 32 years at the former Barnbow Royal Ordnance Factory in Cross Gates.
Richard Noble said: "He is very shocked and very subdued. He is bitterly upset about it.
"He doesn't really care about the money, he just wants his lifetime of memories in the box back.
"He is upset about the whole thing. He is such a nice fella and would welcome anybody in. He is just upset that somebody could do this."
"We are quite a forgiving family, but it's difficult to forgive people who do this to elderly people."
Neil Liversidge, managing director of Castleford-based West Riding Personal Financial Solutions Ltd, is offering a Â£5,000 reward for information leading to the conviction of those responsible and the return of the property.
Mr Liversidge, said: "Mr Noble has been a client of mine for many years.
"He is a gentleman in the truest sense of the word and I regard him as a personal friend.
"When his country needed him to go to war, he put his life on the line for his fellow citizens.
"He is one of the last, and sadly diminishing band of survivors, of what was probably the greatest generation this country ever produced.
"That he should be targeted as he has been is utterly despicable
A West Yorkshire Police spokesman, said: " Enquiries are ongoing regarding the incident which took place during the afternoon of Tuesday July 24 after a suspect attended at the victim’s address claiming to be a water board official.
"The suspect told the victim he needed to check the property for damp and left.
"Afterwards the victim and his family noticed a metal box was missing from the property.
"The box contained cash and a number of irreplaceable items of deep sentimental value.
"Anyone who has information about the incident or who can assist the investigation is asked to contact Leeds District CID on 101 referencing crime number 13180367713
"Information can also be given anonymously to the independent Crimestoppers charity on 0800 555 111."