s the 75 horse-power water-cooled Rolls Royce, it
being considered to be the most efficient for the purpose. The engine
is mounted upon bearers above the level of the top of the car, and
drives a four-bladed pusher propeller.

The car is suspended from an envelope of 70,000 cubic feet capacity,
and the system of rigging is similar to that in use on all S.S. ships.
The petrol is carried in aluminium tanks slung on the axis of the
envelope, identically with the system in use on the S.S.P's. The
usual elevator planes are adopted with a single long rudder plane.

The speed of the Zero is about 45 miles per hour and the ship has a
theoretical endurance of seventeen hours; but this has been largely
exceeded in practice.

The original ship proved an immediate success, and a large number was
shortly afterwards ordered.

As time went on the stations expanded and sub-stations were added,
while the Zero airship was turned out as fast as it could be built,
until upwards of seventy had been commissioned. The work these ships
were capable of exceeded the most sanguine expectations. Owing to
their greater stability in flight and longer hours of endurance, they
flew in weather never previously attempted by the earlier ships. With
experience gained it was shown that a large fleet of airships of
comparatively small capacity is of far more value for an anti-submarine
campaign than a lesser fleet of ships of infinitely greater capacity.
The average length of patrol was eight hours, but some wonderful
duration flights were accomplished in the summer of 1918, as the
following figures will show. The record is held by S.S.Z. 39, with 50
hours 55 minutes; another is 30 hours 20 minutes; while three more vary
from 25 1/2 hours to 26 1/4. Although small, the Zero airship has been
one of the successes of the war, and we can claim proudly that she is
entirely a British product.

S.S. TWIN

During the year 1917, designs were submitted for a twin-engined S.S.
airship, the idea being to render the small type of airship less liable
to loss from engine failure. The first design proved to be a failure,
but the second was considered more promising, and several were built.
Its capacity is 100,000 cubic feet, with a length of 164 feet 6 inches,
and the greatest diameter 32 feet.

The car is built to carry five, with the engines disposed on gantries
on the port and starboard side, driving pusher propellers. This type,
although in the exp