USN photo # 19-N-23871 from the Bureau of Ships Collection in the U.S. National Archives.
Mackerel underway at full speed during builder's trials in Long Island Sound, March 22, 1941. Mackerel had been built with the aft end of her fairwater already cut down, providing an excellent location for an additional M2 .50 caliber water cooled machine gun. She would later have a 3"/50 caliber Mk 6 gun added aft of the fairwater.
USN photo # 19-N-23871 from the Bureau of Ships Collection in the U.S. National Archives.
Close up of the photo above, showing details of Mackerel's original conning tower fairwater configuration. On the top of the covered pilothouse is a mount for a M2 .50 caliber machine gun, similar to the mount on the aft fairwater deck. Her two periscopes and radio mast are protected by fully plated shears. This would later be unplated. A circular LF radio loop antenna is mounted on the aft fairwater deck. This could receive LF radio transmissions while the boat was at periscope depth. The conning tower itself (inside the fairwater) was actually very small (unlike the fleet boats), not much more than an access trunk for the bridge. All of the torpedo fire control equipment was located in the control room.
