Not quite right Supermunk. Military IFF comes in Modes 1, 2, 3, 4 (and maybe 5 now?). Mode 3 is the same as Mode A and you may hear military controllers say 'squawk mode 3/A ****'. As someone else suggested Mode C came along a lot later as a bolt-on-goodie to mode A and so controllers may ask for mode A but really want mode C as well.