Edmund Hadnett writing in his article AIS at the Front Line in the May 2005 issue of the Journal, attributes to me the argument that ‘the automatic radar plotting aid (ARPA) should remain the principal means of assessing a risk of collision’. ARPA has never been the principal means of assessing a risk of collision and I have never argued that it has been and should remain so. My argument concerns the merits respectively of ARPA and AIS as navaids or a fusion of data from both.