Hundreds of serving and former Royal Navy personnel face having their pay packets docked after the Ministry of Defence admitted to a £1.2 million overpayment blunder.
The mistake, which affects 423 sailors, was uncovered on the heels of a long investigation dating back many years in ratings' pay grades.
Those affected will see a shortfall in their pay packets until the debt is settled.
The error is also thought to affect a number of personnel who have either retired or been made redundant.
The MoD said these would also be expected to pay the money back.
One of those affected is understood to have been told that he must give back as much as £17,000.
Meanwhile another member of the service has been asked to give back just £9.
The servicemen affected found out in a letter from the MoD.
The department wrote that an investigation had been carried out, saying: "The findings highlighted over-payment to a number of Navy personnel.
"Any overpayment has been held in suspense while the question of write-off action was considered by the Service Personnel and Veterans Agency.
"Unfortunately it has been decided that write-off to this debt has been deemed inappropriate.
"To that end, all monies owed will now been recovered."
In most cases, repayments will be by instalments through deductions from pay.
Under MoD rules, those affected will not lose more than four days' pay a month.
A spokesman for the MoD said it had apologised to all those affected.
"Where repayment of monies is appropriate, procedures are in place to prevent any hardship to individuals."