At 02:00 local time, Cardiff's operations room detected XX377 on her surface plot radar at a range of 25 nautical miles (46 km).[2] The helicopter's identification friend or foe (IFF) system was turned off, so receiving no friendly transmissions and with the contact apparently heading towards Stanley, the operations room crew assumed it to be hostile.[2] After calculating its speed they believed they were tracking an Argentine fixed-wing aircraft—either a Hercules conducting a resupply mission, or a FMA IA 58 Pucará ground-attack aircraft sent to retaliate for Cardiff's shelling.[2][14][15] Cardiff fired one of her Sea Dart missiles.[16][8] 5th Infantry Brigade lost radio contact with the Gazelle, and simultaneously the exploding missile was seen and heard by the re-broadcast station's personnel atop Pleasant Peak.[9] Cardiff's crew were able to see the fireball, but only with the aid of night vision goggles.