Upvote:6
Doing some more digging based off of the information in Pieter's answer (and not having seen CGCampbell's comment which says this same thing), I found the US Army Ordnance Corps uses the crossed canon and grenade symbiology on their insignia.
The crossed cannons are representative of the Ordnance Corps's early relationship to the Artillery. The flaming bomb, also known as the shell and flame, represents the armament of days gone by, while the energy it connotes is applicable to the weapons of our own day
Upvote:8
Too long to be a comment, though not really a full answer:
This is likely much older than WW2 or even WW1. That shell above the crossed gun barrels is a "bomb bursting in air", and likely dates the ring to before the Mexican American War.
Crossed gun barrels has long been used by the U.S. Army as the branch insignia, historically usually worn on the cap but now elsewhere on the uniform (shoulder?). However when present, all examples I could find with a shell as well had the shell superimposed over the junction of the gun barrels. the style of these gun barrels is also much older than that typical even in the Civil War.
Artillery until very modern times was distinguished as being either Field or Siege, with the latter being much larger and heavier guns.
Sterling is a grade of silver: "containing 92.5% by weight of silver and 7.5% by weight of other metals, usually copper."