SPECIAL NAVAL NOTICES 239
it is dangerous to pass. When black balls are shown at each yardarm
it is dangerous to pass on either side within a distance of at least 900
yards.
Green lights are shown at night in place of the black balls by day.
Single Vessels Approaching Squadrons.—A vessel approaching a
squadron of warships should avoid going amongst them. If unable
to keep out of their way the ordinary Regulations for preventing
collision apply.
Warning Signals to Denote Presence of Submarines.—The vessel
escorting the submarines displays a square red flag. She should be
given a wide berth and, if it is necessary to pass close to the escort,
vessels should proceed at slow speed and keep a sharp lookout for
periscopes.
Aircraft at Anchor show the same lights as surface craft and also
wing tip white lights when the span exceeds 150 feet.
AIRCRAFT.
Information with regard to Distress Signals by Day and Night.—
Mariners and others are notified that when any aircraft is in distress
and requires assistances the following shall be the signals displayed by
her, either together or separately:—
I. The International Signal "SOS" by means of "Visual or
Wireless Telegraphy or in the case of Radio Telephony the
spoken word "Mayday."
II. The International Code Signal of Distress indicated by N.C.
II1. The Distant Signal consisting of a square flag having above or
below it a ball or anything resembling a ball.
IV. A continuous sounding with any sound apparatus.
V. A signal consisting of a succession of white pyrotechnical lights,
fired at short intervals.
VI. A white flare from which at intervals of about 3 seconds a white
light is ejected into the air.
In the event of a distress call being received from "an aircraft in
distress over the English Channel, the position of the aircraft will, be
fixed by directional wireless from the appropriate D.F. stations and a
warning will then* be broadcast to shipping by'North Foreland wireless
station giviag the necessary particulars,—December, 1927.