Although this was written in 1985 about the Falklands War, it has come to stand for many different kinds of solidarity, most recently British Forces in Afghanistan. YouTube views of any version are in the multii-millions; this one, live and while Mandela was still in prison, might still be the most moving.
It is this fellow feeling that infuses the military, more so when things go wrong. Having one's ship torpedoed, being rescued, enduring a POW camp, sitting in an FOB, or in a convoy waiting for the next IED: the rest of us get it intellectually, but not viscerally. Is it the sharing of intense fear – the most heightened emotion – that chooses an anthem? Something about Brothers in Arms has made it anthemic.