The Anti-Motor-Torpedo-Boat (AMTB) 90mm gun M1 on mount M3 was developed in 1941 to provide a weapon that was effective against fast torpedo boats, aircraft, and land targets. It could be controlled manually or automatically through a remote control system. A protective shield was installed around the gun and allowed crew access and gun loading through the rear. Many AMTB batteries were installed in American harbors.The gun pictured in front of Building 600 is a WW-II 90mm Anti-Aircraft piece that was also used in an anti-motor-torpedo-boat (AMTB) role. It appears that this piece is sitting on a AMTB mount. Only about 800 of these were made, and only about 5 or 6 still exist.There were a number of 90mm AMTB batteries in the Harbor Defenses of Los Angeles.
Source Information: website “History of Fort Tilden, NY”; Sam Stokes
Over the years many have wondered about the "gun" mounted in front of Building 600, Shemya, AK. Here's some answers for you. (Our thanks to George Blood for furnishing this picture. You can see more of George's pictures, including this weapon, in his "Shemya Scrapbook.")