On January 4, 2015 I posted an aerial photo from the Panama Canal V. I. P. Slides and dated 7-12-69 produced by the Panama Canal Graphics Branch showing the Gatun Spillway.  I mentioned in my narration this comment: I wonder what the zig zag formations are in the green area just above the dam.  Well as usual, one photo leads to another topic which has kept my mind working since CZ Images contributor Andrew Fraser wrote to me with a possible solution to my question and sent me a map image to prove the solution.  I have blown up and cropped the same photo from January 4 so the zig zag formations can be seen better.  Well the map Andrew sent me shows that there were 3 gun antiaircraft battery sites on each side of the spillway for aerial defense.  See map below.  This is a crop from this old Declassified Secret map shows Battery 7 and Battery 8 on each side of the spillway.  The zig zig earth berms in the photo above are very likely the remains of Battery 7.  The photo doesn't show enough of the other side of the spillway apron to show if any remains of Batter 8 were still there.  Just as a quick side bar, there appears to be some sort of road, railway or foot bridge between each side of the aprons.  I can't imagine a fixed bridge here nor a floating one.  Not sure what this structure is.  It is not shown in the late 1970s photo at the far bottom of this page.  Go figure.  Another thing leads to another thing. The late 1970s photo shows the the berms are pretty much breaking down for some reason but you can still see where that strange bridge connect to the land.

Show below the map is a photo of a 3-inch antiaircraft mount taken in the 1930s.  This is not necessarily one of the 3-inch mounts at Gatun Spillway, but is just like the ones that would have been there.  This photo is from the book The American Defenses of the Panama Canal by Terrance McGovern, published in 1999.  The following narration is also from the McGovern book:

"The actual anti-aircraft defenses were very weak due to demands for guns in the European conflict. Only eight 3-inch guns were mounted by 1918.  Seven of these guns were in fixed mounts around the seacoast defenses and one gun was mounted on a railway car.  Four more guns were received in late 1918 and were emplaced around the Gatun Dam.  In April 1920, thirty-six 3 inch guns were allocated to the Canal Zone,  By 1931, the U.S. Army had emplaced the 3-inch antiaircraft in fifteen 3-gun batteries on fixed mounts (throughout the Canal Zone) and one 3-inch battery on railway cars. Supporting these antiaircraft guns were twenty-nine mobile 60-inch searchlights and sixteen .50-calibre machine guns."

With this information found, this is what the zig zag berms were used for. Can you imagine going back in time and seeing these batteries in full operation defending the Gatun Spillway from aerial attack.  3-inch guns, searchlights and .50 caliber machine guns locked and ready for action.  I only wish I had ventured up in this area in the early 1970s when I lived in Gatun.  I could have seen the berms first hand and taken photos.  But, I think the reason I didn't is that that area was surely off limits on non-lock/spillway workers.

Thank you for your help Andrew.