"ROCKETS!"
Up it went, higher and higher, with a sea of faces upturned to watch it, and then an explosion that seemed
to split the silent night in two, and a shower of stars sank slowly down and went out one by one. And with
a gasping sigh one word escaped the lips of the crowd: "Rockets!"
-  Lawrence Beesley, The Loss of the SS
Titanic
.
From the  "Regulations for Preventing Collisions at Sea" that were in effect in 1912 dealing with the subject of distress
signals:

    When a vessel is in distress and requires assistance from other vessels or from the shore, the following shall be the
    signals to be used or displayed by her, either together or separately:

    At night:
    (1) a gun or other explosive signal fired at intervals of about a minute.
    (2) Flames on the vessel as from a burning tar barrel, oil barrel, etc.
    (3) Rockets or shells, throwing stars of any colour or description, fired one at a time at short intervals.
    (4) A continuous sounding with any fog-signal apparatus.

According to Wreck Commission Report into the loss of SS
Titanic, there were a total of 36 socket distress signals carried
on board in lieu of guns. As described by the manufacturer of these socket distress signals, the Cotton Powder Company,
Ltd., they were "a substitute for both guns and rockets in passenger and other vessels." And Lloyd's Calendar yearly
remarked: "Socket distress signals are fired from a socket, ascend to a height of 600 to 800 feet, and then burst with the
report of a gun and the stars of a rocket." (Leslie Reade,
The Ship That Stood Still, Patrick Stephens Limited, 1993, Ch.
4.).

As
Titanic's First Offer Lightoller explained during questioning at the British Inquiry:

14150. Now, then, about signals from your boat. You have rockets on board, have you not? Were they fired? -
[Lightoller] You quite understand they are termed rockets, but they are actually distress signals; they do not leave a trail of
fire.
14151. Distress signals? - Yes. I just mention that, not to confuse them with the old rockets, which leave a trail of fire.
14152. Those are distress signals? - Actual distress signals.
14153. What sort of light do they show? - A shell bursts at a great height in the air, throwing out a great number of stars.
14154. What is the colour? - Principally white, almost white.
14155. How are they discharged; are they discharged from a socket? - In the first place, the charge is no more and no less
than what you would use in a 12-pounder or something like that. In the rail is a gunmetal socket. In the base of this
cartridge, you may call it, is a black powder charge. The hole down through the centre of the remainder is blocked up with
a peg. You insert the cartridge in this socket; a brass detonator, which reaches from the top of the signal into the charge at
the base, is then inserted in this hole. There is a wire running through this detonator, and the pulling of this wire fires that,
and that, in turn, fires the charge at the base of the cartridge. That, exploding, throws the shell to a height of several
hundred feet, which is nothing more or less than a time shell and explodes by time in the air.
14156. Had you yourself anything to do with sending up these distress signals? - No, my Lord.
14157. Did you hear any order given about them? - No.
14158. You merely saw they were being sent up? - Yes.
14159. I think it was Mr. Boxhall, who is here, who had something to do with sending them up? - I believe so.
14160. Did you notice at all how many were sent up or at what intervals? - I should roughly estimate somewhere about
eight at intervals of a few minutes - five or six minutes, or something like that.
14161. One at a time? - Yes, all fired from the starboard side, as far as I know.

As Lightoller pointed out, these socket signals were not like the old rockets which had a propellant which produced a long
trail of fire as they went aloft. Instead, they were launched by an exploding detonator from a socket which sent an
explosive shell aloft several hundred feet. The shell had a timed burning fuse which did leave a faint streak as the shell
went up. The fuse then set off a large explosive charge in the shell after it reached several hundred feet aloft which then
burst into stars.

Titanic's Third Offer Herbert Pitman witnessed the firing of Titanic's rockets soon after he left the ship in lifeboat No. 5.
As he explained to Senator Smith at the American Inquiry: "I should say about a dozen rockets were fired...They were
fired from the rail. They make a report while leaving the rail, and also an explosion in the air, and they throw stars, of
course, in the air." When asked if those were red in color, Pitman replied that he saw "various colors" in them.

Titanic's Fifth Officer Harold Lowe described seeing Bruce Ismay in the flash of one of these distress signals after he
started to load lifeboat No. 3, soon after boat No. 5 was sent away:  "I distinctly remember seeing him alongside of me -
that is, by my side - when the first detonator went off. I will tell you how I happen to remember it so distinctly. It was
because the flash of the detonator lit up the whole deck, I did not know who Mr. Ismay was then, but I learned afterwards
who he was, and he was standing alongside of me...they were incessantly going off; they were nearly deafening me."

Titanic's Fourth Officer Joseph Boxhall was personally involved in firing these distress signals. As he explained during
questioning at the British Inquiry:

15395. How many rockets did you send up about? - I could not say, between half a dozen and a dozen, I should say, as
near as I could tell.
15396. What sort of rockets were they? - The socket distress signal.
15397. Can you describe what the effect of those rockets is in the sky; what do they do? - You see a luminous tail behind
them and then they explode in the air and burst into stars.
15398. Did you send them up at intervals one at a time? - One at a time, yes.
15399. At about what kind of intervals? - Well, probably five minutes; I did not take any times.
15400. Did you watch the lights of this steamer while you were sending the rockets up? - Yes.

As Boxhall explained to Senator Smith at the American Inquiry: "The rockets are exploded by a firing lanyard. They go
right up into the air and they throw stars...I fired them just close to the bows of this emergency boat [boat No. 1 on the
starboard side]...these distress rockets are dangerous things if they explode, and I had to keep people away clear while I
fired the rockets." When Boxhall was asked as to the character of the rockets, as to their color, he replied: "Just white
stars, bright. I do not know whether they were stars or bright balls. I think they were balls. They were the regulation
distress signals." When asked about how these signal would appear at a distance, Boxhall replied: "It is the first time I have
seen distress rockets sent off, and I could not very well judge what they would be like, standing as I was, underneath
them, firing them myself. I do not know what they would look like in the distance."

But there was a witness who saw what these distress socket signals looked like at a distance. It was
Californian's young
Apprentice James Gibson. In a signed statement written to Capt. Lord on April 18, 1912, while
Californian was still at sea
heading for Boston, Gibson wrote: "I then got the binoculars and had just got them focused on the vessel when I observed
a white flash apparently on her deck, followed by a faint streak towards the sky which then burst into white stars." This
was written just 3 days after the event took place, before anyone other than those on the
Californian knew that rockets
were seen from
Californian's bridge that night. Since Gibson was able to first see the flash of the detonator that fired the
shell aloft, his unbiased observation clearly proves that
Californian was near enough for Titanic's boat deck to be seen
above the visible horizon from where they were located.

The timed sequence of photographs seen below shows a typical shell being sent aloft and bursting into stars. Notice that
the bursting shell is principally white in color, but a few other colors can be seen in the spreading stars as they start to fade
away.