The Information Commissioner's Office (ICO) has ordered the Minstry of Defence (MOD) to improve its response to requests under the Freedom of Information Act.
The Act requires a prompt response to requests, but an ICO audit found that a number of the MOD's internal reviews had taken longer than 40 working days to complete.
In one case, a requester was kept waiting for over 190 working days for a response from the MOD, the ICO said.
The ICO has issued a practice recommendation to the MOD for failing to complete internal reviews within a reasonable time.
The ICO guidance states that a reasonable time for completing an internal review is 20 working days and no case should exceed 40 working days.
Gerrard Tracey, assistant information commissioner, said the ICO would monitor the MOD's performance over the next year.
Failure to conform with the ICO's recommendation will result in closer scrutiny of the MOD's performance.