[mopee167]

I think the initials on the cover of Speed Comics #37 (May 1945) that look like "JC” are actually "JK”... which would make that cover as being drawn by a young Joe Kubert (age 18).

[The Australian Panther]

mopee167,

That's a nice cover! Thanks for bringing my attention to it. I like group covers.
When you mention a book or books it's helpful if you include the link in your post so others can quickly access it.
Just click on the link in the browser, click copy and then paste onto the page.
https://comicbookplus.com/?dlid=25846
Well done to find that signature. Took me a while.
This is what GCD says about that cover,
https://www.comics.org/issue/4372/

Although a previous indexer credited Rudy Palais with the art, the initials 'J C' are clearly visible. Comparing this with the signed cover to #39, the styles are different. On #39 Palais does not yet know the physical details of either Captain Freedom (note neckline, size of star of forehead) or, in particular, The Black Cat, who looks very little like what has gone before. In summary, this is NOT Palais. 

 
You will note that Joe Kubert is credited with the inks on the Black Cat story. Over Jill Elgin's pencils.
Note her mask in that story, and you will see that the Black Cat on the cover must be by a quite different artist.
There is nothing on this cover that is in Kubert's art style - which is hard to disguise. Note that GCD does not dispute that the initials are J. C. 
Personally , I think that the cover is a mash-up of the work of many artists, since each character is drawn in the style of the artist of it's books. J.C. may have penciled in the postions on the cover.     

[mopee167]

I tried to  post the comment on the appropriate page but I kept getting an error message.

I still think the entire cover is by Joe Kubert. The difference in Black Cat's mask in the interior story would be due to Miss Elgin's pencils, if she did indeed pencil the story.

Also Jerry Bails Who's Who does not list anyone working at Harvey at the time who had the initials J.C.

Thanks for putting up the link.