Joseph Allen, 70, raided Poppy Appeal collection tins to steal £10,000 destined for former servicemen, Amersham Crown Court heard.
He stole the rest of the cash by writing cheques made out to himself.
Allen, of Paterson Road, Aylesbury, admitted four charges of theft and was handed a 16-month sentence.
The former treasurer for the Buckinghamshire Royal British Legion branch had served in the forces for 15 years and was a volunteer with the charity for 20 years.
He wrote 23 cheques worth £16,000 out to himself over a three year period, forging countersignatures so as not to raise suspicion, the court heard.
Allen was told he had abused his position to commit a gross breach of trust.
Laura Blackband, prosecuting, said: "He was of course allowed to write cheques from that account to cover legitimate expenses but these were unexplained," she said.
"They were not supported by any expense claims and he could not explain why they had been written."
Allen also took cash straight from collection tins from 2011 to 2013.
Ms Blackband said: "This was money he had failed to pay into the (British Legion) bank account. He appropriated the cash from the tins."
Tim Nutley, defending, said Allen had initially been motivated by his £13,000 debt to a mortgage company and money owed on credit cards.
"He also spent part of the money [he stole] on two holidays which he went on with his wife to Turkey," he said.
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A British Legion treasurer who stole more than £26,000 from the charity to pay off debts and fund holidays to Turkey has been jailed.