Oberon, I was not on Blue Steel and only have an outline of the system. In the final run the missile would indeed been on its own. Prior to that a series of radar fixes would have been taken and a procedure based on fix-monitored-azimuth performed. Essentially was the missile inertial navigator properly aligned. Was its stable table stable. Values of kE and kN would be input and inertial drift minimised.
While the launch point was not as important as a bomb release point it was still important as it would determine the safe route for the missile.