depth rating 1000 m -> ~10.1 MPa external.
Al 6061 cylinder, rough: t/r >= P*r/(sigma_allow). with safety 1.5 and
sigma_allow ~150 MPa, t/r ~ 0.1 -> for r=0.265 m, t ~ 27 mm. heavy.
syntactic foam for buoyancy trim. composite option? ask David, he hates Al here.
buckling, not yield, probably governs. DO THE BUCKLING CHECK before quoting t.