A steam vessel shall be provided with an efficient whistle or siren, sounded by steam or by some substitute for steam, so placed that the sound may not be intercepted by any obstruction, and with an efficient fog horn, to be sounded by mechanical means, and also with an efficient bell. (In all cases where the rules require a bell to be used a drum may be substituted on board Turkish vessels or a gong where such articles are used on board small seagoing vessels.) A sailing vessel of 20 tons gross tonnage or upward shall be provided with a similar fog horn and bell.

  In fog, mist, falling snow, or heavy rain storms, whether by day or
  night, the signals described in this article shall be used as follows,
  viz: 

  (a) A steam vessel having way upon her shall sound at intervals
  of not more than two minutes a prolonged blast.

  (b) A steam vessel under way, but stopped and having no way upon
  her, shall sound at intervals of not more than two minutes two prolonged
  blasts, with an interval of about one second between them.

(c) A sailing vessel under way shall sound at intervals of not more than one minute, when on the starboard tack one blast, when on the port tack two blasts in succession, and when with the wind abaft the beam three blasts in succession.

  (d) A vessel when at anchor shall at intervals of not more than
  one minute ring the bell rapidly for about five seconds.

(e) A vessel at anchor at sea, when not in ordinary anchorage ground and when in such a position as to be an obstruction to vessels under way, shall sound, if a steam vessel, at intervals of not more than two minutes, two prolonged blasts with her whistle or siren, followed by ringing her bell, or if a sailing vessel, at intervals of not more than one minute, two blasts with her fog horn, followed by ringing her bell.

(f) A vessel when towing shall, instead of the signals prescribed in subdivisions (a) and (c) of this article, at intervals of not more than two minutes sound three blasts in succession, namely, one prolonged blast followed by two short blasts.  A vessel towed may give this signal, and she shall not give any other.

(g) A steam vessel wishing to indicate to another “The way is off my vessel; you may feel your way past me” may sound three blasts in succession—­namely, short, long, short—­with intervals of about one second between them.

  (h) A vessel employed in laying or picking up a telegraph cable
  shall on hearing the fog signal of an approaching vessel sound in answer
  three prolonged blasts in succession.