ough
the air at such speed is not conducive to a careful scrutiny of the
surface of the water below, necessary in order to detect the vague,
dim outlines of a submerged submarine. At first the pilots of naval
aeroplanes had considerable success in locating the submarines, and
Germany lost quite a few of them, before the reason was discovered.
Some one in Great Britain announced that it was easy to locate a
submarine from an aeroplane by the peculiar reflection in the sunlight
caused by the fine film of lubricating oil on the surface of the
water. As soon as this "tip" was communicated to Germany, submarines
discontinued the use of oil for lubrication, employing instead
deflocculated graphite. The fuel oil used in the Diesel engines for
propulsion on the surface is so thoroughly consumed and the exhaust
now is so free of oil that an oil film as an indication of submarine
proximity is no longer trustworthy. Besides, the submerged boat
_might_ be a friendly one, a fact which was borne upon the British
authorities on two separate occasions when scouting aeroplanes
reported submarines near, and speedy motor boats rushed to the attack.
In one case the British submarine is reported to have been rammed, and
in the other--so the story goes--the commander of the submarine
liberated a little buoy attached to the outside of the boat, which
rose to the surface and informed the watchers above that "a friend is
down below--not an enemy!"

The system followed now in the locating and possible destruction of
German submarines in the Channel and North Sea by French dirigibles is
as follows: The airships, chiefly of the _Astra_ type, travel at a
height of not more than 500 feet above the surface of the ocean, while
the observers constantly sweep the water within a radius of half a
mile with their glasses. Usually the airships are sent ahead at low
speed in spirals, or in a series of curves which enable them to cover
every square mile of watery area below. As soon as one of these
airships sights a submarine traveling submerged, it flashes the news
by wireless to destroyers which at the time may be fifty or more miles
away, and in the meantime endeavors to remain directly above the
submerged boat. Soon the destroyers arrive and, following the
direction of the airship, can ram or sink the submarine with almost
certain success. The French admiralty claims to have accounted for a
number of submarines by this method, but has found that the sche