Apologies if this is too specific, but I'm working through my grandfather's letters back home during WW2, and in one he goes into detail on a protective coating he called "cogmodine" (he admits he doesn't know how to spell it) which was used to preserve tanks and other machines as they crossed the ocean. Apparently it had to be carefully removed after landing and he claims he saw instances of the material getting the way of combat operations on multiple occasions. He refers to it as a sort of black tar.
He has unfortunately passed away so I'm not able to ask him directly. Any help would be appreciated!
I think he's talking about Cosmoline. It's a wax-like preservative that goes on wet like oil but when dried, becomes a thick coat of dark brown sludge. It was used extensively in the late 19th century all the way up to the Cold War. It's still available now but I'm not sure if it's used for preservation in the military. It is a highly effective preservative that stops the element from corroding military equipment; Soviet surplus guns dug out of decades out storage can be restored to like-new condition by just removing the Cosmoline. However, they are the bane of gun and militaria collectors everywhere because they are a major pain in the rear to remove. Theoretically they melt in heat, but even after a thorough disassembly and cleaning, you will still get Cosmoline "sweating" out of the wood stocks or out of the internals for no reason after months of use; it gets bloody everywhere.
I'm not surprised that he saw Cosmoline get in the way of combat operations. A common failure of Russian SKS (semiautomatic rifles from 1945) dug out of surplus is slam firing caused by Cosmoline. The goo gets into the firing pin channel and freezes the firing pin in the forward position. If not cleaned properly, the gun can become runaway full automatic as the momentum of the bolt moving forward to chamber a round slams into the back of the cartridge and ignites, firing every single round in the magazine in quick succession. This can be extremely dangerous and draw uncomfortable gazes from people on the range next to you.
The only difference I can see between his account and my experience is the colour of the goo. Everything I've seen is a dark brown, deep chestnut colour, not black. That may just be a turn of phrase, or maybe whatever gunk, sand, soot or dust that accumulates on the Cosmoline at its application in a US loading facility is a different colour to Soviet arsenals.
Cosmoline. It was ( and is- it's still made) a very dark brown waxy petroleum grease. The original stuff had a petroleum solvent, and when new was not too hard to clean off. But once that solvent outgassed, the resulting coating became pretty tough. It can still be found adhering to a variety of old military surplus equipment, everything from steel tow cables, spare lug nuts for trucks.... even soaked into old cordage for tarps. There seems to have been a mania for applying it. If you'll check this old manual for the Browning .30 Machine Gun, you'll see it was recommended for preventing corrosion from a gas attack, and Army veterinary manuals recommended it to cover wounds on horses
Other countries used the stuff as well. Doing a brief search I located a couple of Turkish Mauser sights for sale coated with it, that give you a pretty good idea of what it's like.
If you want to do a deep dive into Cosmoline ( shudder) the original spec sheet is here:
http://everyspec.com/MIL-SPECS/MIL-SPECS-MIL-C/MIL-C-11796_NOTICE-1_49856/