The Defence department has been keeping a secret list of its costly blowouts and delays.

Defence has had a “projects of concern” list for over a decade, listing its worst-performing military acquisitions. A recent Quarterly Performance Report from the Department's Capability and Sustainment Group has been obtained by the ABC.

Much of the detail was redacted on “national security” grounds.

One of the biggest projects on the concern list is the ADF's MRH90 helicopters.

Australia plans to spend $3.5 billion on 47 new MRH90s — a multi-role helicopter to replace the Sea King and Black Hawk fleets.

The MRH90 fleet is currently limited on certain missions because its auxiliary power unit does not allow the main engines to be shut down.

Other concerns were raised with amphibious ships, new air combat capability and light protected mobility vehicles.

Australian Strategic Policy Institute senior fellow Andrew Davies said Defence is struggling to deliver capabilities on schedule, and is being unnecessarily secretive.

“Defence has been getting more and more secretive, or less transparent, year by year for the last decade or so,” Dr Davies told the ABC.

“The redactions in the report are on the grounds of national security, and that might be fair enough for some of the capability issues they're facing — you don't want to flag to an adversary that you're having trouble getting your equipment to do such and such a task.

“But things like project schedule and budgets ... it's very hard to see how they're really of any national security importance.”

The Australian National Audit Office slammed Defence's growing levels of secrecy especially in relation to problems with major projects, in a report earlier this year.

“Over the last five years, transparency has reduced, the level of formality has declined with explicit criteria replaced by unpublished principles, and processes have become less rigorous with a greater emphasis on maintaining relationships with industry,” the ANAO wrote in March.