Danish soldiers will be required to shoot first and ask questions later if the United States invades Greenland, under the army’s rules of engagement.On Wednesday, the Danish defence ministry confirmed the existence of a 1952 rule requiring soldiers to “immediately” counter-attack invading forces without awaiting orders.The defence ministry also said that the rule “remains in force” when asked about its status by Berlingske, a centre-Right Danish newspaper.This week, Donald Trump, the US president, has repeated his intention to annex the Nato territory of Greenland, which he views as essential to US national security, including by military force if necessary.