         let φ1 = toRadians(lat1)
         let φ2 = toRadians(lat2)
         let Δλ = toRadians(lon2-lon1)
-        let R = 6371000.0 // gives d in metres
+        let R = 6371000.0 // gives distance in meters
         let distance = acos(sin(φ1)*sin(φ2) + cos(φ1)*cos(φ2) * cos(Δλ) ) * R;
         
         return distance

    var enemies = [Enemy]()
    
    let enemyRadius = 2 // Kilometers
    let shootRadius = 200.0 // In meters
    
    var enemiesLoaded = false


    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let gunFireFile = NSBundle.mainBundle().URLForResource("fire", withExtension: "mp3")
        do {
