SINKING THEORIES: FACTS AND HYPOTHESIS OF THE CAUSES OF THE SINKING OF THE CONFEDERATE SUBMARINE H L HUNLEY

There have been numerous discussions in the CSS H L HUNLEY CLUB and in the press around various theories about the sinking of the Confederate Submarine H L Hunley. I have tried to compile these theories, excerpted from our discussions to condense them to an abridged form.  I have also tried to give credit where credit was due, but in many cases there were conjoining parts and pieces on theories scrambled with original thoughts mixed with known facts. The task at hand was not as easy as I thought it would be so no one take offense. I have had the advantage of being able to look at all the theories and the disadvantage of not having all the facts. Can any of the theories be ruled out? I think with most of them only parts can be rejected in time. The article starts with some of the facts that we know from the information that was provided, editorial privileges and b.s. (biographical sampling). A little logic and familiarity with the waters of Charleston Harbor, the help of the experts in the “Club”, and information from the “Friends of the Hunley, Inc.” make these facts fairly secure.

In this newsletter, the reader has the opportunity to choose the Sinking Theory that he or she thinks the best, most logical, most likely or closest to what actually happened on the night of February 17, 1864. The reader may also choose to add their own theory. I have started out with known facts including the physical and mechanical justifications to these facts, have given other opinions when appropriate and then numerated and captioned the various theory categories. PLEASE VOTE ON THE THEORY OF YOUR CHOOSING and I will let you know the outcome next newsletter.  Believe me it won’t be easy.

THE FACTS:

#1 The snorkels were discovered in the upright position. There were consistent problems with the snorkel and air bellows.

#2 The rudder was found completely underneath the sub.
#3 The Hunley was found approximately 650 feet from the wreckage of the Housatonic.
#4 The Hunley did not sink lying on her starboard side but somewhere in time rolled over. There was an unexplained cannonball size hole and a gash on the starboard side. The Hunley when discovered was found rested on her starboard side. • “The two holes on the starboard side of the hull appear to not be contemporary to the submarine's sinking. McConnell said both holes could have been made by an anchor that was dragged across the hull of the sub before it was covered in the silt.” The analysis of the Hunley interior sediments shows that several hull penetrations happened years latter after the sinking.......................... http://gsa.confex.com/gsa/2001AM/finalprogram/abstract_28473.htm
 "After initial sedimentation of fine-grained materials with rare bivalves and later filling of relatively coarse shelf
materials, in situ shells indicate a calm period of little to no deposition. Afterwards, another episode depositing shelf-reworked fauna added additional materials to the sub", may show the results of separate events that cause the large hole in the stern and one of the other holes. “
#5 The lower spar was bent possibly from the impact with the Housatonic or from the crash dive.
#6 The crew was in all probability seriously hurt from the explosion which happened less than 150 feet away.
#7 A “blue light” signal was seen from the Housatonic and Battery Marshall. “Blue lights were common signals used by both sides. We also know The lantern found on the Hunley is definitely not blue. The lens was not covered in concretion and clearly visible to the naked eye.

#8 The Hunley was not operating as a submarine, but more as a “David” a surface semi-submersible vessel when it sunk the USS Housatonic.

#9 Dixon knew the tide schedule when he departed Sullivan’s Island and had developed a mission time table. The Hunley could not make headway against the tide so everything had to be timed perfectly. 

 ADDITIONAL FACTS:

This final crew had only been together three months, had practiced the long dive, lengthy runs,  and strenuous cranking periods. We know from information that has been released that the aft hatch is latched closed. The forward latch is not engaged, latched nor closed all the way and an x-ray shows the hatch is slightly opened a small amount, less than one degree.  The fact that the hatch was closed but not latched either indicates a forced or sudden dive or that Dixon may have unlatched it at the last moment to attempt an escape.

 Ballast tanks, at the bow and the stern were flooded by valves to submerge and pumped dry by hand to resurface. The Iron ballast keel could be jettisoned by unscrewing the heads of the bolts from inside the submarine.

There was air in the upper portion of the cabin interior for an extended period indicating there were no significant leaks.

WE KNOW THAT DIXON AND HIS CREW COULD NOT TELL IF THEY WERE MAKING FORWARD MOTION WHILE SUBMERGED

McClintock admitted that his boats suffered from three basic problems: the lack of a self-propelling motive power, inaccurate compass readings, and an inability to measure the horizontal movement while running submerged.

"...One difficulty which Mr. McClintock very frankly pointed out was the uncertain action of the compass in such a vessel...He also pointed out another requirement which he had not succeeded in applying - rather from want of means than from want of skill, or from any great difficulty in the requirement [illegible]. He states that when under weigh beneath the surface, it is quite impossible to ascertain whether the vessel is progressing as there are no passing objects by which to recognize the fact of motion; on several occasions when experimenting with his boat they continued working the crank while all the time the boat was hard and fast in the mud ("Report on a submarine boat invented by Mr. McClintock of Mobile, U.S. of America," PRO, Adm. Series 1/6236, File 39455).

NOTICE THE SCALE OF THE HUNLEY COMPARED TO THE DEPTH OF THE WATER

Analysis of the sediment and degree of preservation indicates that Dixon was covered before the rest of the crew, indicating a possible leak from the forward area or did a sudden dive cause the stern ballast tank to empty forward.

We do know that the crew was not all at their stations.  The two crewmen right behind Dixon moved forward and the two men farthest aft moved aft we assuming to work the aft pump. One crewman was found closer to the top, a possible indication of an escape attempt. None of the others made an effort to escape. The majority of the crew showed no indication of awareness that the sub was mortally sunk.

* In an endurance test dive, the crew of the Hunley sat on the ocean bottom for two hours, thirty-five minutes without surfacing for air.

crew quietly losing consciousness and dying of oxygen deprivation.

Did they all go to sleep to never wake up.    The crew members have been found at their work stations. This suggests there was no panic on board. Scientists half- expected to find the bones of the crewmen mingled on the floor of the sub as they died climbing over each other trying to open the sub's hatches. The remains have been found in neat intervals in the mud.
 Stalactites and oxygen stains that suggest that the sub's interior did not fill with water right away, shooting a hole - so to speak - in the single-bullet theory.

The only crewman not found at his seat was found on top of what may be the remnants of a bellows used to pump air into the Hunley. He could have been trying to suck new air into the sub when it went down.

Doctors deduce the crew may have died from anoxia, a complete lack of oxygen. If that occurred, the crew would have simply run out of oxygen and gone to sleep.

THEORIES "WHY DID THE HUNLEY SINK?"

 (I) Dixon miscalculated...One theory is in maneuvering for the attack, backing away, and avoiding the sinking Housatonic, Dixon found himself farther from base than he planned and was faced with the prospect of going across the paths of ships coming to the rescue rather than away from them so he took the Hunley down. Did Lt. Dixon
(1) Intentionally take the Hunley down to wait for the tide to turn.
(2) Submerged  to rest the crew and perform first aid  or
(3) Submerge to allow the Yankee rescue efforts to subside.

(II) RUNNING SUBMERGED WAITING IT OUT   The theory that the Hunley may have been running submerged or waiting it out on the floor of the harbor for the Canandaigua and other rescue vessels to leave the area has been discussed.  We know that the interior stayed dry by evidence of the stalactites that allows us to conclude that there was air in the 25’ of cabin area that lasted for years.
Maria Jacobsen has stated that it was not possible for Lt. Dixon to look out the hatch portholes when the latch was engaged. “You can’t fit your head in the conning tower with the latch locked down.  Therefore Dixon left it unlatched for surface operations.”  It certainly seems unlikely that Dixon would have intentionally gone for the bottom with the hatch unlocked.

The bones were found near the front of the sub, slightly behind and just a foot below the front hatch that opens through the top of the sub. "We had never expected to find human remains at this high level," said Jacobsen, who works inside the sub in a space so cramped she can barely move her head up and down. "That is a huge surprise."

The time Dixon’s watch stopped supports this theory.
Sen. Glenn McConnell, chairman of the Hunley Commission, says the watch supports one longtime theory. “I believe the apparent time suggests the watch out-lived the crewmen and continued to tick for many hours past their deaths,” McConnell said. “It also raises the supposition that the submarine may have remained less than flooded long after the demise of the crew. If the submarine had flooded shortly after the attack, it seems probable the watch would have stopped at a time closer to, but after 8:45 p.m., when the attack on the Housatonic occurred.”

(III) EQUIPMENT MALFUNCTION  including malfunction of the snorkel valves or the dive planes. One theory offers the possibility that this equipment had mal-functioned that night unbeknownst to the crew and that the oxygen was reduced and anoxia had set in with the effect of decreased ability to make sound decisions.  The lack of oxygen theory has as much merit as any. When the candle went out after a half hour the crew may not have responded correctly to this vital signal. What stage of anoxia would the crew have been in when the air in the boat could no longer support a candle flame?

"One or both hatches may have been opened for use of the blue signal lamp (a blue calcium)  It certainly seems unlikely that Dixon would have intentionally gone for the bottom with the hatch unlocked."

"If the Hunley was still able to make headway, Dixon's crew would have been cranking for their lives. They wouldn't have been concerned about the direction as long as it was toward safety..
b_rogoff … "I agree with the theory that something went wrong with the prop or rudder or both. Otherwise, the Hunley would have been long gone by the time the Canandaigua showed up. If either the rudder or the prop
was damaged, it could help to explain why the boat was found further out to sea than the Housatonic."

"After the detonation, the crew would have been cranking backwards like crazy, probably harder than they had even cranked before. (They were getting shot at after all.) Dixon would have been trying to control the rudder and to adjust the trim at the same time."

"The torpedo lanyard would have indeed been trailing the boat. If the boat was backing in a curve, the lanyard would have been dragged along the same curve. When the boat reversed course, it could have run right over the lanyard, which might then have been sucked through the fairing into the prop. (Reminds me of the Caine mutiny when Queeg
(Bogie) ran over his own line.)"

"In any case, Dixon might have sent someone over the side to try to repair the damage IF he knew what needed to be done. Or perhaps it simply couldn't be repaired."

"Or perhaps he didn't know about the damage. That would mean that the fate of the Hunley's crew was a cruel one. Imagine cranking at top speed for 45 minutes, expecting to be well on your way home, and then discovering that you've been going in circles. You're still in danger of being spotted and attacked and actually getting further out to sea"…..Barry

 ************ 

The Hunley controlled her depth using a combination of things: the ballast tanks and the dive planes and forward motion. The normal mode of operation was to trim the tanks to neutral buoyancy and then use the planes to control the depth once the propellers were turned or by motion from gravity. An equipment failure in any one of these systems could be catastrophic.

If the propeller shaft was damaged the dive planes were rendered useless without forward or reverse motion. Without the command to close the hatches and latch them down and the boat started diving, Dixon and his First mate would have had to react. A sudden 45 degree dive would cause water to spill out of the ballast tanks into the crew compartment expediting the unexpected dive. (Remember the sub is almost 40’ long in 27’ of water.)  The sub would suddenly be in a dive mode whether forward or reverse and before the action could be stopped, the Hunley would have hit bottom in the shallow water around the battle area. Now to surface the crew would have to release the ballasted keel.  The keel release mechanism may have failed as it did in the second Charleston Harbor sinking.
 

 ************

(IV) SWAMPED - the men opened the hatches for air as they began their return and a wave washed over the sub and swamped it. This may have been one of the reasons for the first sinking.

The Hunley was struck and fatally damaged by another Union ship that was coming to the rescue of the Housatonic - Did the Canandaigua come along and swamp her?  This theory includes that the Hunley was swamped by waves on its return journey.
 (V) Single-bullet theory (Lucky Shot) surmises that a Minie ball fired from the deck of the USS Housatonic shattered the Hunley's forward cast-iron conning tower during the attack, allowing water to pour in while an injured Lt. George Dixon struggled to control the contrary sub. This theory has been disproved due to air left in the sub after she sank. A conning tower hole would have quickly allowed the sub to fill with water, but some people still think it’s feasible..
(VI)  The Hunley was destroyed by the same explosion that sank the Housatonic?  “Was she drawn into the vortex of the sinking sloop”

This theory that the Hunley was sucked into the Housatonic was disproved upon her discovery in 1970 by Dr. E. Lee Spence.
The following letter confirms that many believed this idea to be true before then.

Letter from Captain Gray, C.S. Army, to Major-General Maury, C.S. Army,
regarding the loss of the H.L. Hunley and her crew.

Major-General DABNEY H. MAURY,
Mobile, Ala. (excerpt)
          The United States sloop of war was attacked and destroyed on the night of the 17th of February. Since that time no information has been received of either the boat or crew. I am of the opinion that the torpedoes being placed at the bow of the boat, she went into the hole made in the Housatonic by explosion of torpedoes and did not have sufficient power to back out, consequently sunk with her.     I have the honor to be, general, very respectfully, your obedient servant, OFFICE SUBMARINE DEFENSES, Charleston, S. C., April 29, 1864 M. M. GRAY,
Captain in Charge of Torpedoes.

 ************
D. D. Porter's history of the war states explicitly that HUNLEY was sucked into the hole blown in the Union ship,
and dragged down with it. He states clearly that she was found that way, with all her crew drowned.

“Frankly, I've never been entirely comfortable with the assumption, based mainly (entirely?) on the blue light reportedly seen on shore, that HUNLEY actually survived the attack. Of all the scenarios for the boat's loss I've read, none seems as likely to me as the boat being sunk/mortally damaged by the explosion of her own torpedo.” -----------> AH

 (VII) SANK IN A GALE:     Senator McConnell announced that there is evidence to be released that the Hunley may have been lost the night of the sinking in a gale. The intimation was that the Hunley after signaling its success to the troops at Battery Marshall may have been swamped by a wave from the sudden gale. This may have caused water to flood into the open hatches, causing the Commander to suddenly go below, closing the hatch, but not locking it down,  Proceedings of a court of inquiry convened on board the USS Wabash, February 26, 1864

First. That the U. S. S. Housatonic was blown up and sunk by a rebel torpedo craft on the night of February 17 last, about 9 o'clock p. m., while lying at an anchor in 27 feet of water off Charleston, S. C., bearing E. S. E., and distant from Fort Sumter about 5½ miles. The weather at the time of the occurrence was clear, the night bright and moonlight, wind moderate from the northward and westward, sea smooth and tide half ebb, the ship's head about W. N. W. “…………..The mast of the ‘Housatonic’ are all that can be seen of her, and the gale which is now prevailing will do much to make a complete wreck of that once noble ship”

But further research shows that eyeball testimony lugs a strong load on the scale of truth. One of the surviving sailors from the Housatonic wrote a letter to the Boston Herald that ended up in the Charleston Mercury on March 14, 1864. The letter in part states, “The event took place about 9 o’clock on one of the coldest nights of the winter.”.

We know from varying accounts and from personal experience that the weather in Charleston Harbor in February is cold and can get severe in short order without notice. The old Charleston Daily Courier reported that "several ironclad's were seen to anchor at Light House Inlet off Morris Island after dark to escape the rough seas off shore."

In a letter by Augustine Smythe, sailor from the C.S.S. Palmetto State dated February 21st, 1864 states "The submarine torpedo boat - The Fish - which has been put in repair and been lying down at Sullivan's Island for some time, went out on Thursday night and it is supposed, sunk a blockader, as one of them was seen to go down.  This attack was unknown at the time even at Head Quarters.  They supposed it was the storm.  Since then however, nothing has been heard of her and she is put down as lost. 

So there are snippets of information that indicate the possibility of some time of severe weather in the Harbor the night of the sinking of the USS Housatonic and the Confederate Submarine H L Hunley. It may have been that a gale or storm in the area may not have been significant or of note at the time within the scope of all the other war activities that were going on. We have the advantage of knowing that the design of the Hunley made it vulnerable to wave action or rolling particularly if the hatches are open. You may recall that one of the theories around the first sinking of the Hunley at Fort Johnson evolved around the possibility that the wash or wake from the C.S.S. Etiwan set into motion that sinking.

 (VIII)   SUICIDE An agreement was made among the crew that if the Hunley ever got stuck on the bottom under water they would open the seacocks and end it all.  They had decided that they would rather drown quickly at their own choosing than suffocate slowly.  We have not been provided with information about the seacocks and what position they were in. Due to the fact that there was air in the sub long after it sank pretty much rules this out..

 In the TNT cable network movie "The Hunley," the crew floods the disabled sub, choosing death by drowning rather than slower death by suffocation. 

(IX) DETONATING TETHER FOULED THE PROPELLER 

"After the Hunley’s torpedo detonated, it left somewhere between 50 and 150 feet of detonating tether strung out ahead of the boat. As a natural fibre material, fully saturated, this cord probably had near-neutral or slightly negative buoyancy, and would begin trailing aft as the submarine began to move forward again and picked up speed."

 "Assuming (as I believe to be correct) that the tether reel was a simple spool affixed to the hull near the forward hatch; the reel could neither be rewound from inside the boat nor jettisoned entirely. In those circumstances, the remaining tether would likely begin trailing aft from the reel, back along the shoulder of the boat's hull. It seems distinctly likely to me that this could result in the cord becoming fouled in the screw, and possibly jamming it altogether."

 "The latter scenario would, in my view, be almost certainly fatal to the boat and crew. Without its forward motion to literally drive it to the surface, the Hunley’s crew would have to achieve positive buoyancy within the boat. This may he been difficult to do, particularly if the boat settled on the bottom with a substantial list (as she was ultimately found). William Alexander described how, on the boat's earlier "endurance" dive, they very nearly didn't get off the bottom due to one of the two pumps clogging. It also would likely have been very difficult to unbolt the keel weights in the extremely dark and crowded interior of the submerged boat. Also, although there is no clear evidence of a massive, fatal injury to the craft now apparent on the wreck, one should not discount the possibility of numerous small leaks caused by the concussion of the torpedo. Propelling the boat to the surface may have been their only real hope of staying afloat, and with the torpedo tether wound securely around the screw, they may well have been without any propulsion at all." AH  Tigone

TIDE CHART TIMELINE – THE NIGHT OF FEBRUARY 17, 1864

Remember that weather conditions affect tidal ranges and current speeds, sometimes very strongly.

*Add in the fact that they were probably less than 250' away from the Housatonic on the tail end of the ebb tide, causing them to drift away off-shore. The incredible force and pressure from the blast would have caused near un-consciousness and confusion, if not killing a few of them. The blast effect could have caused the propeller to turn in reverse (if not geared) breaking or bruising arms or legs. Waves of water from the blast and the ocean would have added to the weight of the ship and soaked the freezing crewmen. The remaining crew would have to make a turn toward shore, the blacked out blockade runners are now lit up or visible, and the decision to dive (against the standing order not to submerge) is made.

** We know from witness accounts that a blue light signal was seen. Was it a signal from the Hunley or a danger signal given by the Union forces?
Was a lamp signal given by the Hunley and if so was the hatch fully closed afterwards or did Dixon try to get the hatch open to escape after the Hunley was sunk.

***Two pieces of a thin (5.6 mm in diameter) glass tube, the remains of the submarine's depth gauge were found concreted to the submarine's hull near Lt. George Dixon's post. If this was shattered as a result of the explosion then Dixon had no way of knowing how deep he was.

 “I would imagine that submarining around, or "waiting it out" on the
 bottom, with an unsecured hatch is not a Standard Operating Procedure……...” yello_armadillo

”In the end, I think that the damaged shroud and rudder are going to be key.  Somehow, the rudder was detached from the sub (thus it being found underneath the Hunley).  I suspect that the rudder was damaged, either by the explosion or by a collision with one of the rescue vessels.  “

”They may have spent the 45 minutes before help arrived trying to repair the damage on the surface before diving to avoid detection by the rescue ships.  Or, without a rudder and/or a damaged propeller they might have drifted with little or no control over the direction, and submerged to avoid being swept out to sea.  “

”At any rate, I think they ended up on the bottom alive and died of lack of oxygen some time later.  I think the presence of the stalactites tells us that they didn't drown.” "Ian Chafee", 16 Sep 2002

 ************

“The point I've been trying to make about the Hunley is that avoiding detection was not a valid reason for submerging the boat and sitting on the bottom after the attack. There was a period of about 45 minutes in which there were no other vessels in the area that could have spotted the Hunley on the surface and Dixon surely knew that. Had be been able to take advantage of that opportunity to escape on the surface, he would have”….Barry

  ************

“Mission Plan: Hit and Run or Hit and Hide?  I think the evidence tilts away from a planned dive to the bottom, but doesn't rule out an emergency dive that went wrong”.  "jvnautilus" Michael

 ************

“It seems plausible that as had been done in practice, that the captain allowed the boat to go to the bottom to allow time to pass before attempting the escape. He has already signaled to the shore and was prepared to make the run after a reasonable time had passed.”

“Let’s assume that he waited until the air became reasonably untenable and then ordered the tanks to be pumped. Now is where my questions about the pumps come in.”

“How many strokes could be made before the air is exhausted.  It could be that it would be impossible for the pumps to be worked enough with the air remaining to get water out as fast as it was coming in, or in the worst case, depending upon the characteristics of the pumps to pump at all because of the pressure difference.”  "Donald Gerue"9 Sep 2002”

 ************

“And don't forget that the crew was probably injured and deafened by the premature explosion. Either of those things would have had a serious effect on their morale. Imagine sitting there in the dark with your hands on the crank and being unable to hear the captain or even the man next to you. Anyone would feel panic under those conditions.”

”There's a big difference between actively doing something to save your life, like cranking for shore, and crouching inside a cold iron tube, shivering, and waiting for something to happen that may or may not improve your chances of surviving, like the tide turning or the rescue vessels leaving. Dixon was well aware of all these things and I think he would have chosen to allow those men to try to save their lives no matter what theoretical advantage there may have been to waiting.”   Barry

  ************

“The discussion about the blue light is interesting. Another way of interpreting it is that they were moving underwater for over a half hour and came up to get their bearings to land and to see what had happened.  While the one man stood in the hatch, watching for the bonfire, he saw a ship in the area and also that they had not gone far.. Capt. Dixon, assessing the state of his crew, and worrying about the ship nearby, thought that the best course was to go to the bottom (which I am assuming he knew the depth,). They closed the hatch went to the bottom  and when the time came they found they could not ascend.”  Don Gerue

  ************

***********************************************************************

BLUE LIGHTS WERE COMMONLY USED BY BOTH SIDES DURING THE CIVIL WAR

Report of Lieutenant-Commander Whiting, U. S. Navy, commanding U. S. S. Ottawa.

U.S. GUNBOAT OTTAWA,
Off Charleston Bar, January 22, 1863.

SIR: I have the honor to report that last night at about 10:40 p.m., while at anchor off the Swash Channel, a schooner was made standing out between us and the bar.

Being in readiness to slip, I allowed her to approach so as to draw her out from the channel way. When underway I steamed toward her, cutting off the retreat which was attempted. She was brought to with a shot from the 20-pounder Parrott, which struck in the port bow, bursting and doing some damage.

On boarding she proved to be the schooner Etiwan, of Charleston, S.C., just out from there. The master, A. O. Stone, reports the cargo to be 99 bales of cotton and 2 barrels of resin. She has a crew of five men. I enclose a report to the district judge, with the papers found on board.

I would respectfully report that while in chase of the Etiwan and nearing her, the Housatonic fired across our bows, I suppose intended for the schooner. I sent up a rocket and showed the red light on the side toward her. A second shot was fired from her about the time our shot was fired at the schooner, which passed over our mastheads. I immediately hoisted the running night signal lights. A few minutes after, while lowering a boat to board the prize, a third shot was fired from the Housatonic, which passed directly over the quarter-deck, abaft the mainmast. A blue light was then burned to show the position of the vessels, finding that the regular running lights were not sufficient.

At the time we were fired upon the Powhatan and Quaker City were visible with the glass in their stations and the Housatonic distinct with the naked eye.

It is to be supposed that our identity was not sufficiently marked to protect us from the fire of a blockading vessel, which I hardly need add might have proved exceedingly disastrous; but as I employed all the preconcerted signals, I could do no more.

Very respectfully, your obedient servant,

 WM. D. WHITING,
Lieutenant-Commander.

 Captain S. W. GODON,
U.S.S. Powhatan, Senior Officer Present.

*The schooner “Etiwan” should not be confused with the 132 ton CSS Side-wheel steamer “Etiwan”. It is ironic that on April 4 (or 6), 1863 the CSS Etiwan, aka Etowan, Etowah, Etwan, or Hetiwan exploded a torpedo (mine) under her hull and just before sinking, intentionally ran aground near Fort Johnson less than a hundred yards from where the first sinking of the confederate submarine H L Hunley, August 29, 1863 occurred. The CSS Etiwan was repaired held some responsibility for this sinking in Charleston Harbor. The Etiwan ran aground again in the same area, June 7, 1864 and was shelled by the new Union batteries set up on near by Morris Island. After the war the wreck of the Etiwan was repaired by the Federal government and she was renamed the Saint Helena.

"In case of an alarm, a blue light will be burned; in case of an attack, a rocket will be sent up."

"Blue lights burned at night by our tug packets indicate the approach of the enemy."

I immediately gave orders to beat to quarters and slip the cable, firing a rocket and burning a blue light in the meantime as a signal of alarm.  Almost at the instant a vessel was seen to the N. N. W. of us, distant 300 yards, burning a blue light, which is known to be the signal of distress.....................

General order of Rear-Admiral Porter, U. S. Navy, embodying instructions to blockading vessels off Eastern and Western bars.

GENERAL ORDERS,
No. 18.

The signal for danger will be the firing of a gun and the burning of a blue light.

I have therefore to request that a supply be sent, as also blue lights, if the signal for danger be not changed.