: "...polish the cannon balls."

"...polish the cannon balls." Where did the phrase 'no need to polish the cannon balls' come from. I have heard it used to indicate over preparation.

It's not a phrase I am familiar with, but I assume it comes from the fact that polishing cannon balls is a rather pointless activity: adding a needless refinement.
DFG

In the British Army it was traditional to whitewash the coal before an important inspection. (VSD)

Is that actually authenticated? I have always assumed that it was something of a myth, and that those completely pointless tasks, if performed at all, were performed as a punishment.

After all, why would any high-ranking visitor be anywhere near any place the coal was kept? It probably isn't most Generals' idea of a good time to inspect the cellars.

DFG