Radio tower: “Check fuel Fortis 1 and 2” [honestly not sure if he says Fortis or Portis, or something else, but anyway he’s asking what the fuel gauges say in each of Lowden and Hardy’s planes]
Hardy: “70 gallons”
Lowden: “68 gallons, Fortis leader” [I think he says leader, as in he’s in the lead plane]
Next scene, Lowden beginning to panic at the German plane on his tail
Lowden: after looking around and checking his rear view, sees German plane behind him and says: “He’s on me”
Hardy: “I’m on HIM” [all cool and calm, like he’s got it all under control]
So, to clarify (not sure if this is too much detail, sorry), there’s three planes: Lowden is first, then the German plane, then Hardy’s plane. Basically the German plane is all over Lowden’s plane waiting to get him in its sights so they can take Lowden out, but Hardy sets his plane behind the German plane to take them out before the German plane can take down Lowden
Hardy, now behind the German plane, does some maneuvering to get the German plane in his sights. Takes a few shots and misses.
Hardy tells Lowden: “On my mark Fortis 2, turn left….3…2…1…MARK”
Lowden quickly jerks his plane to the left in order to get the fuck out of the way of the incoming bullets, so Hardy can take out the German plane without getting his own ass lit up.
As soon as Lowden is out of harm’s way, Hardy shoots again and hits German plane and says “Clear” [I think?]
Lowden: “Is he down?”
Hardy: “Yeah, he’s down for the count”, he says as they watch the German plane crash into the water
Then Lowden asks Hardy: “Fortis 2, what’s your fuel?” [He would have done this being concerned about Hardy’s fuel, even though Hardy had two more gallons than Lowden at the start of the scene – Lowden knows damn well that with all the maneuvering Hardy had to do with his own plane in order to take out the German, he would have been running low on fuel and likely be running on fumes]
Hardy answers: “My gauge took a bit of a knock” [camera shows the gauge glass all cracked and busted up]
Lowden: “Shouldn’t you turn back?”
Hardy: “No, no….fairly confident it’s just a gauge” [meaning that he knows better than a damn gauge]
Then the end scene where the propeller stops, Hardy looks at it, and he’s probably crapping his pants because he ran out of fuel, and also – he’s annoyed that he was wrong [I’m gonna guess that he’s as arrogant as fuck in this film so he’s probably more annoyed that he was wrong than anything else] (just my opinion)
Also, I think the switching back and forth between which plane is Fortis 1 and Fortis 2, is likely due to the fact they would have considered whichever was in first communication to be 1 and the plane they were addressing to be 2, so it would have depended on who was talking to whom, and not necessarily one of the planes being designated as 1, and the other designated as 2 (If that means anything to anyone – and also I could be wrong, but if I am, then they just fucked it up because they both were referred to as ‘Fortis’ 2 at least once)
