Towards the end of 1909 a new aluminium alloy was discovered,
known as duralumin. Tests were made which proved that this new
metal possessed a strength of twenty-five tons per square inch,
which was over twice as strong as the nominal strength of
aluminium, and in practice was really five times stronger. The
specific gravity of the new metal varied from 2.75 to 2.86, as
opposed to the 2.56 of aluminium. As the weights were not much
different it was possible to double the strength of the ship and
save one ton in weight. Duralumin was therefore at once adopted.

The hull structure was composed of twelve longitudinal duralumin
girders which ran fore and aft the length of the ship and
followed the external shape. The girders were secured to a steel
nose-piece at the bow and a pointed stern-piece aft. These
girders, built of duralumin sections, were additionally braced
wherever the greatest weights occurred. To support these girders
in a thwartship direction a series of transverse frames were
placed at 12 feet 6 inches centres throughout the length of the
ship, and formed, when viewed cross-sectionally, a universal
polygon of twelve sides. For bracing purposes mesh wiring
stiffened each bay longitudinally, so formed by the junction of
the running girder and the transverse frames, while the
transverse frames between the gasbags were stiffened with radial
wiring which formed structure similar to a wheel with its
spokes. The frames where the gondolas occurred were strengthened
to take the addition weight, while the longitudinals were also
stiffened at the bow and stern.

Communication was provided between the gondolas by means of an