clusively. Approximately as many were
turned over to the army during the year, each one being slightly
improved. Zeppelin and his staff of experts were always able to profit
by the practical experience which the ships were undergoing almost
daily.

Zeppelins Become Lighter and Stronger

The hulls were strengthened and made more rigid, yet lighter, machine
guns were mounted at proper points of vantage and bomb dropping
apparatus so perfected that heavy loads of explosives could be carried
in absolute safety, yet instantly released and with remarkable accuracy.
An observation car was added to each new ship.

The Zeppelin Observation Car

This car was one of the most unique inventions developed during the war.
It could be lowered with an observer aboard, fully one kilometer (3,280
feet) below the Zeppelin. Here the observer could get his bearings while
his ship lay far above hidden in the clouds. The ship could fly or drift
above the clouds to a point directly over the spot to be bombed, then by
lowering the car with the observer through and just below the clouds, he
was able to direct both the operations of the ship and the bombing. A
telephone connection ran up through the supporting cable. He was able to
signal for bomb releases and navigate so efficiently that any objective
could be attacked without danger of the enemy seeing the Zeppelin
lurking behind the clouds.

Another Zeppelin, the L-20 was delivered to the navy early in 1916. It
had hydrogen capacity of 1,271,160 cubic feet (36,000 cubic meters)
though the diameter was the same as the others. The L-20 carried a
useful load of 37,478 pounds (17,000 kilograms), and an increase of
1,312 feet (400 meters) over their ceiling and made the same speed with
the same horsepower.

During the year Zeppelin delivered seven more ships of this type, but
possessing greater efficiency. The navy received five of them and the
army two.

[PLATE 19: Maybach Airship Motor of 145 Horsepower, 1911.

Maybach Airship Motor of 180 Horsepower, 1913.]

Anti-Aircraft Defenses Compel Zeppelins to Fly Higher

The Allies meanwhile had developed anti-aircraft defenses and their
airplanes possessed greater climbing ability. To meet these new
conditions the airships were continuously compelled to fly higher. They
also required speed greater than the average of 54 miles per hour (25
meters per second) because while navigating over the North Sea they
frequently encountered