Boy, am I out of my element here. However, I must say that the artillery sites that ringed San Francisco Bay, the area I live in (unfortunately), had some of what I believe were called “disappearing cannons” during WWII, when some thought that there would actually be an invasion of the West Coast by the Japanese. These big guns could only be seen above the parapet (right word?) when they were about to be fired, or were being fired. They recoiled back and down with the muzzle below the parapet, I think, for loading. I believe that this type of gun goes back to the Civil War (or before???).
If I’m all wrong, let me know. I was born in 1939, and have no real memory before VJ Day, which I do remember. However, some of the guns were still there for a little time after the war, as I recall. Wow - a lot of years since then.
There is a nice paper-back book, “Artillery at the Golden Gate, The Harbor Defenses of San Francisco in World War II,” by Brian B. Chin, that mentions these guns, I find, but doesn’t seem to picture one. They do picture some of the various artillery pieces used, and even a guy sitting behind a Model 1917 Water-Cooled Browning Machine Gun. The book was published in 1994 by Pictorial Histories Publishing Co,., Inc., 713 South 3rd Street of Missoula Montana 59801. When I bought it, it was only 12.95. I think I got mine at the Fort Point Museum, Fort Point, San Francisco. The fort sits right under the south end of the GG Bridge, and was designed by the same military architects that designed Fort Sumter.