Whose drone was flying near these oil tankers that were attacked in the Gulf of Oman, reportedly causing Iran to fire a missile at it, and what was its mission?

This was a drone controlled by members of the Mercenary Army Program. There are many operations done under the aegis of the intelligence agencies. This is shared with the U.S. Military Command so there are no misinterpretations and cross-interference with their plans, but because of the top-secret nature of what is being done and why, this will not be clarified in the public domain. There may be a cover story appear down the line by those who think this is simply an aspect of military intelligence gathering who are not privy to the deeper, darker reason that this was carried out, but the reality is it was in support of the black project involving the attack on the oil tankers.