40MM Anti-Aircraft Battery

These emplacements were, surprise(!), for taking down enemy aircraft that made it past the 5" guns. There 40mm mounts all over the superstructure of the Massachusetts, just as on all battleships during the war. There were so many in fact, that after the war, the Massachusetts had three of them removed during a refit that no other ship of its class got. If you visit the USS Alabama, these mounts are still in place, along with a slew of 20mm guns all over the ship that the Massachusetts had removed during the post-war refit. The removed 40mm mounts were on top of the #2 turret (it partially blocked the view from the pilot house), and two mounts were forward on the fo'c'sle.

Here you can see the remnants of the 40mm mount (and two 20mm mounts) on top of the #2 16" turret.

A better view looking down on the #2 16" turret from the pilot house. Two holes on the sides were where the 20mm guns were located, between them was the 40mm mount.

The guns are quad-mounted in 15 emplacements scattered around the ship. The ammunition was loaded via 4 round magazines per rifle. That may sound like too few shells per magazine, but the firing rate per rifle was just slow enough for the ammo handlers to keep these things fed during a fight. Initially the crew had to make numerous runs back and forth to the ammo lockers to keep these guns firing, but later there was a modification made to the splinter guards (shields around the gun mounts) to allow small amounts of ammo storage at each mount.

Front view of the splinter guard.

Those slots were used to hold extra magazines locally. Seen inside the splinter guard.

Look closely and you'll see what looks like where additional magazine brackets were once welded to the inside of the splinter shield.

These guns, like the other guns on the ship (excepting the 20mm AA guns) are radar directed. There are electric motors on the base of these mounts to move them when under radar control, but they can also be controlled locally in case the radar direction system goes down.

Here is a shot of a radar director for the 40mm mounts in it's sector.

The mounts on top of the 16" turrets are the ones that amaze me. From what I've been told from a modern day dreadnought sailor who served on the USS Missouri in the late 80's/early 90's, the decks were largely cleared when the big guns blazed. During an air attack, I guess the big guns wouldn't be firing, so the 4omm crews wouldn't be exposed to the concussion of the blast.

Here is a shot of the 40mm mount on top of the #3 16" turret.