Original caption: 10/6/1939-Canal Zone,Panama:War in Europe has resulted in a general tightening of the defenses of the Panama Canal,vital lifeline of the U.S. in the event the trouble should spread across the two oceans.Particular attention has been paid to anti-aircraft defenses of the"Big Ditch."Concentration of searchlights in action. It would be a lucky & agile mosquito who could fly over here without being caught in one of the pointing fingers; the guns that act in concert with the lights would do the rest.