The Royal Australian Navy’s fleet of six Collins-class submarines will likely necessitate substantial upgrades to remain in service until the new SEA 1000 submarines start arriving, navy chief Vice Admiral Mike Noonan indicated at an Australian senate hearing.

“We’re expecting that we will upgrade at least five, and the work around determining the scope of the upgrade has begun but has not yet been fully decided,” Australian ABC News quoted the Vice Admiral as saying.

The Collins-class boats had previously been expected to start retiring from 2026. This has changed, however, as the old boats will have to remain in service until the Attack-class submarines start arriving.

The new subs will be built by France’s Naval group who is expected to deliver the first unit in 2032. The project to deliver 12 new submarines will cost an estimated AUD 50 billion.