The audit, published on Monday, is the second into the department's use of travel and meal expense accounts in four years, and also highlighted the department's failure to act on some of the recommendations of the previous report.

It found the department had still not established appropriate and effective controls to ensure accurate travel allowances were paid to eligible employees of credit card use worth some $93 million last fiscal year.

The allowances are paid to Defence employees and public servants to cover travel costs, meals and incidental expenses when travelling for work, but the governance of the credit cards has repeated come under scrutiny in recent years.

"[The audit office's] analysis indicated that Defence's preventative controls are not fully effective, with Defence unable to provide documented approvals for 21 per cent of the sample travel allowance transactions reviewed as part of this audit," the report said.

"Defence has progressively implemented detective controls since July 2017, in the form of credit card compliance activities, and expects that these activities will continue to evolve to address emerging and ongoing risks."

The audit office found that despite a review of the department's red tape in 2015, five of the 20 recommendations made had not been completed. The department reported 10 had been to its enterprise business committee.

The 2015 review described the department's travel policy and procedures as a "frightening smorgasbord of documents", yet it seems the department is still yet to act on several key proposals of the review.

But the audit office found that as of February, the department's travel policies still included four policy documents, three joint directives, seven policy guidance documents, 16 intranet pages, 15 fact sheets, two quick guides, two checklists and 27 credit card management system guidance documents.

Despite the plethora of travel policy related documents, the audit office reported finding gaps, inconsistencies and ambiguities throughout the material.

The audit office also previously made two recommendations to improve the department's use of credit cards in 2016, but despite the department telling the audit office it had implemented the changes in 2016, the latest audit found one recommendation was only partially implemented and the other was still in the process of being put in place.

The department responded to the audit office's report, saying that through its own internal review processes, it had already started work on a number of initiatives to improve its administration and oversight of travel allowances and associated travel card processes.

"Defence has been actively improving the administration of travel allowances, making significant progress in the last six months," the department said.

"Some improvement initiatives were delayed pending the introduction of the travel requisition and expense management system project that was being relied upon to introduce a range of new controls. Following testing, this project has now ceased."

The department also created a travel board in May to bring together the groups responsible for overseeing travel spending. It will govern travel policy, controls processes and compliance.

The audit office recommended the department review its travel guidance documents to eliminate duplication and inconsistency and promote compliance with the relevant policies, and ensure its policy on travel was accurately reflected in the relevant documents.

The report shows the audit was focused on travel cards, rather than all allowances, partly as it had application to all government agencies, because Defence had identified one instance of fraudulent use of a credit card and the audit office has found non-compliance in the department's travel cards in recent years.