Everything anyone knows about the Hunley’s last signal rests on three statements, and they do not say the same thing.

The first is in the Confederate record. On 19 February 1864 Lieutenant-Colonel O. M. Dantzler, commanding Battery Marshall on Sullivan’s Island, reported that the torpedo boat had gone out on the night of the 17th and not returned, and that “the signals agreed upon to be given in case the boat wished a light to be exposed at this post as a guide for its return were observed and answered.” He did not say what the signals were, or when, or who saw them. The report was late because his officer of the day for the 18th “was under the impression that the boat had returned, and so informed me.”

The second is in the Union record. Robert F. Flemming, a landsman and the lookout who had first seen the boat, told the court of inquiry on the Wabash that after the sinking, “when the Canandaigua got astern, and lying athwart, of the Housatonic, about four ships lengths off, while I was in the fore-rigging, I saw a blue light on the water just ahead of the Canandaigua, and on the starboard quarters of the Housatonic.” The Canandaigua reached the wreck at 9.35 by her own log, about three quarters of an hour after the explosion. No one else on either ship is recorded as having seen a light.

The third is a recollection of 1866 by Jacob Cardoza of Charleston, as the Friends of the Hunley quote it: “The officer (Dixon) in command told Lieutenant-Colonel Dantzler… if he came off safe he would show two blue lights. The lights never appeared.” That is the opposite of what Dantzler reported two days after the event.

What a blue light was

For most of the twentieth century these sentences were read with a lantern in mind: a lamp with a blue glass, shown from the forward hatch. Clive Cussler’s first search in 1980 reasoned from that lantern. A blue lantern could not have been seen from Battery Marshall at much more than a mile, so the boat must have been lost close to the shore, and the search went there; she was found fifteen years later four miles out, beyond the Housatonic.

Christopher Rucker, a physician in Spartanburg with a long interest in period artillery and pyrotechnics, made the case in the Civil War Monitor that the lantern is a modern invention. In 1864 “blue light” was the name of a pyrotechnic composition, a hand-held flare used for signalling at night and a required stores item on United States warships; the dictionaries and sailors’ word books of the 1860s define it so. The early recipes had included ingredients to colour the flame, which is where the name came from, but by the war the army and navy ordnance manuals had dropped them, and the composition they specified burned with a brilliant white light while keeping the old name. The 1861 United States manual and Gorgas’s Confederate manual of 1863 both give the recipe. Rucker made it up from them, burned it under conditions like those of the night of 17 February, and found it visible over the four miles between the wreck and the battery. On that reading, Dantzler’s signal, Cardoza’s “two blue lights” and Flemming’s light on the water can all be the same thing: a flare, white, burned from the boat on the surface forty-odd minutes after the attack.

The lantern recovered in May 2001 near Dixon’s remains was conserved in 2012. It is a dark lantern, the kind with a sliding shade to hide the light, and its glass is clear. The Friends of the Hunley’s own timeline says its purpose “was likely to help light the crew compartment.”

What it would mean

If the light was hers, the boat survived the explosion by at least three quarters of an hour, on the surface, with someone alive to open a hatch and burn a flare, and whatever killed the crew happened after that. The Friends’ page on the evidence draws the next inference: the light was “just ahead” of the Canandaigua, which was steaming to the wreck; the boat had no ports facing aft; a steam sloop passing close by could have swamped or struck a hull with three inches of freeboard without anyone on the ship noticing.

If it was not hers, there were other lights on the water that night: the Canandaigua burned Coston signals and sent up rockets as she slipped her cable, and the tug Daffodil came out from inside the bar before midnight. The Lance study of 2017, which concluded from scaled blast tests that the crew “was instantly killed by primary blast trauma,” took note of the eyewitness reports of a blue light and set against them that “eyewitness reports are notoriously unreliable especially in the heat of battle,” pointing out that the Housatonic’s crew could not agree on the state of the tide or the direction of the current.

The physical evidence does not settle it either way. The forward hatch was found unlatched and the after hatch locked; the hatch was heavy enough to stay shut under water on its own, and the Friends do not treat the unlatched hatch as proof that it was opened. The pumps were not set to clear the crew compartment. The keel blocks were in place. The men were at their stations. If a flare was burned, it was burned by someone who then sat down again.

What the Confederate record says, and all it says, is that signals were seen from the shore and answered with a light, and that the boat did not come to the light.

Sources

• Report of Lieutenant-Colonel O. M. Dantzler, Battery Marshall, 19 February 1864, and the abstract log of the Canandaigua for 17 and 18 February 1864, in Official Records of the Union and Confederate Navies, series I, volume 15, pp. 332 and 335. archive.org
• Testimony of Robert F. Flemming, landsman, to the court of inquiry on the Wabash, February 1864, National Archives, Records of the Judge Advocate General (Navy), M273, roll 160, case 4345, transcribed by Rachel Lance on the Vernian Era site. vernianera.com
• Friends of the Hunley, “The Evidence,” “Top Possible Theories” and “Scientific Timeline,” for the Cardoza quotation, the Canandaigua theory, the hatches, the pumps and the lantern. hunley.org, theories
• Christopher D. Rucker, “The Myth of the H.L. Hunley’s Blue Lantern,” Civil War Monitor, citing The Ordnance Manual for the Use of the Officers of the United States Army (1861), p. 307, Josiah Gorgas’s Ordnance Manual for the Confederate States (1863), p. 293, Smyth’s Sailor’s Word Book (1867), and the Associated Press report of 19 April 2012 on the conserved lantern. civilwarmonitor.com
• Rachel M. Lance and others, “Air blast injuries killed the crew of the submarine H.L. Hunley,” PLOS ONE, 23 August 2017, discussion. journals.plos.org