During war, adversaries often go to great lengths in order to gain knowledge of their enemy’s weapons and systems. Technical information, particularly identification of weaknesses, often leads to tactics or weapons to counter the system. It’s called Technical Intelligence or TECHINT, if you are into military acronyms. Some of this knowledge comes from the “spy” sort stealing plans or manuals. Additionally, TECHINT may be derived from debriefing personnel who’ve seen the weapon system in action. But the best TECHINT is to actually have the hardware in hand. For example, from the Cold War, the Central Intelligence Agency recovered part of a Soviet submarine from the bottom of the ocean. However, more often the hardware is acquired on the battlefield. The classic example of this is the capture of a Japanese “Zero” fighter during World War II, which facilitated development of tactics specifically to defeat it in combat.
Though maybe not as exciting as a Zero doing aerobatics or submarines recovered from the ocean, there are many examples of TECHINT from the Civil War. I’ve mentioned Confederate observers posted to watch the monitors on the Ogeechee during the bombardments of Fort McAllister. More an example of debriefing observers as they looked for a weakness in the weapon system in action. During the Petersburg operations, Colonel Henry Abbot collected Confederate projectiles fired into Federal lines and provided a detailed examination. And around Charleston, there was much TECHINT effort focused on the Confederate obstructions and torpedoes. Perhaps the best man in the entire US Navy for such a job was Rear-Admiral John Dahlgren. And his reports to Washington offer many examples of TECHINT gathering. One such report, sent on November 8, 1864, described a device recovered just past the outer end of Maffitt’s Channel:
I transmit a sample of rope cut from a buoy just taken up.
I had gone out of the roads to examine more closely the locality and track whereby the blockade runners pass and was near to one of the wrecks, close into Long Island, when a floating object was perceived which looked like a torpedo. It was picked up, and on examination found to be precisely similar to the floating torpedoes, but had neither fuze nor powder, which puzzled me as to its purpose.
On cutting the rope attached to it there was found a wire rope within, from which was taken the inclosed sample; it is evidently intended to convey a galvanic current and was floated by buoys.
It must have required a great force to part this rope, and was probably done by some steamer passing out of the usual course.
Under the circumstances it is to be presumed that communication was with some one of the fixed torpedoes, and if so, most probably with one that is said to have been lately put down near Sumter.
The telegraphic wires are all sunken on the bottom, as reported by deserters who have had to do with them.
We see Dahlgren was very quick to isolate the probable use of this buoy and cable. He did not speculate as to why the Confederates would adopt a buoyed line as opposed to earlier torpedo control lines sunk to the bottom. There’s a lot of possibilities, particularly wear and tear (communication lines, always in use, are easy to test… on the other hand, the only way to test a control line to a torpedo after it is in place would involve triggering the device). But it is the employment which offered the Federals some advantage. Knowing how to spot the control lines attached to buoys on the surface could allow the ships to avoid the torpedo itself. Or, perhaps allow the sailors to clip the control line and thus neutralize the torpedo. In this case, knowing how the enemy employed the weapon was valuable TECHINT.
Not the sort of stuff found in a saucy spy novel, but these little bits of TECHINT were very much valuable information during the Civil War.
(Citation from ORN, Series I, Volume 16, pages 44-45.)