So the monarch can not veto. Then is the monarch a rubber stamp?
I know you have said that the monarch can send measures back to Commons but only with the advice of the PM. That would still sound as if the monarch has no true power, only that which is "approved" by both PM and Parliament.
The Invasion of Grenada, codenamed Operation Urgent Fury, was an invasion of the island nation of Grenada by the United States of America and several other nations in response to the illegal deposition and execution of Grenadan Prime Minister Maurice Bishop. On October 25, 1983, the United States, Barbados, Jamaica and members of the Organization of Eastern Caribbean States landed ships on Grenada, defeated Grenadian and Cuban resistance and overthrew the military government of Hudson Austin.
The invasion received a mixed reception, although it enjoyed broad public support in the United States as well as in segments of the population in Grenada. October 25 is a national holiday in Grenada, called Thanksgiving Day, to commemorate this event. Conversely, the invasion was criticised by the United Kingdom, Trinidad and Tobago and Canada. Approximately 100 people lost their lives.
International opposition and criticism
Grenada was part of the Commonwealth of Nations and — following the invasion — it requested help from other Commonwealth members. The invasion was opposed by the United Kingdom, Trinidad & Tobago and Canada, among others.[7] British Prime Minister Margaret Thatcher personally opposed the U.S. invasion, and her Foreign Minister, Geoffrey Howe, announced to the House of Commons on the day before the invasion that he had no knowledge of any possible U.S. intervention. Ronald Reagan, President of the United States, assured her that an invasion was not contemplated. Reagan later said, "She was very adamant and continued to insist that we cancel our landings on Grenada. I couldn't tell her that it had already begun."
After the invasion, Prime Minister Thatcher wrote to President Reagan:
This action will be seen as intervention by a Western country in the internal affairs of a small independent nation, however unattractive its regime. I ask you to consider this in the context of our wider East-West relations and of the fact that we will be having in the next few days to present to our Parliament and people the siting of Cruise missiles in this country...I cannot conceal that I am deeply disturbed by your latest communication."
The Organisation of Eastern Caribbean States (OECS) appealed to the United States, Barbados, and Jamaica for assistance. According to Mythu Sivapalan of the New York Times (October 29, 1983), this formal appeal was at the behest of the U.S. government, which had decided to take military action. U.S. officials cited the murder of Bishop and general political instability in a country near its own borders, as well as the presence of American medical students at St. George's University on Grenada, as reasons for military action. Sivapalan also claimed that the latter reason was cited in order to gain public support.
from Wikipedia
By the way, I know several of those former medical students whose records were lost in the upheaval. Thay had the option to begin all over again in another university or just not to become doctors.