I was in the Royal Australian Navy for 10 years, including 2 on Brisbane and I've never slept in a hammock. The Brisbane had 'racks', the after seamans mess had about 30. This image must be some kind of temporary awning used by the demolition crew, possiblily as a shelter from the sun or to contain debris from the explosions. The last Aussie warship with hammocks was probably Diamantina which was de=commissined shortly after I joined in 1974.
