If this question isn't relevant, feel free to remove mods.

Given the nicknames M3 Lee, M3 Stuart, M3 Grant, and M4 Sherman, why were Union and Confederate general names given to tanks, or any modern weapons for that matter?

Follow-up question: Was it common knowledge among Americans that the M4 medium tank was nicknamed the Sherman by the British?

It was never commonly called the Sherman by American forces during the war, it wasn't until after the war that the name was adopted by the Americans. To the Americans the Sherman was the M4 or M4 Medium for much of the war.

It was the British who gave the Sherman that name^1 and used it in official documents, so for the British an M4A1 was a Sherman II while an M4A4 was a Sherman V.

The Americans in general did not name their tanks until late in the war. Names like Wolverine for the M10 and Priest for the M7 were all inventions of the British and in the case of the M10 it was not a popular name. If I recall correctly the M24 Chaffee was the first American tank to officially have a name attached to it by the Americans.

^1 Steven Zaloga - Armored Thunderbolt, pg. 34

Edit: According to this post by solipsistnation the name Wolverine for the M10 was a post war invention, I was always under the impression that it was a name invented by the British but it was one that never stuck. I have edited my post to reflect that.

/u/TheHIV123's answer is correct from my research but many Southerners still hold a lot of resentment towards Union Generals and Military Governors. Some southerners still dislike Sherman, for his march to the sea and destroying Atlanta, and Benjamin Butler, Political Governor of New Orleans and Union General, calling him Beast Butler because of declaration of slaves as contrabands of war during the Civil War.