The 40mm gun was the best anti-aircraft gun to come out of World War II. Designed by the Bofors Company of Sweden, the gun was built in single, twin, and quadruple mounts. Often called the “Bofors Gun,” it had a maximum range of 33,000 feet (6.25 miles) and fired 160 rounds per minute. The guns used fixed ammunition and the two pound shells were held in clips of four and fed into the tops of the guns. They were used primarily for surface-to-air combat, for shore bombardment, for engaging smaller water craft, and for destroying floating mines.
The KIDD is fitted out with fourteen 40mm guns contained in three twin Mk-1 mounts and two quad Mk-2 mounts.
Twin 40mm Gun Mounts 41 and 42 are located forward on the 01 Level just aft of 5-inch Gun Mount 52. The ready service ammunition for the guns was stored in a locker behind the starboard gun. Ammunition racks would also be located on the splinter shields surrounding the gun tub. The gun crew consisted of seven men for twin mounts: the gun captain, a pointer, a trainer, and four loaders. The guns were controlled remotely by Mk-51 gun directors which were located on the Bridge level above. The director computed the lead required to hit a moving target. The men stationed on this gun were basically along for the ride, with the exception of the loaders and the gun captain. But as with most other equipment aboard a destroyer, there were backups for the backups. Should the remote directors fail, the pointer and the trainer would take over the job of moving the gun into firing position manually, using ring sights for aiming.
The two quad 40mm gun mounts aboard the KIDD—Mounts 43 and 44—are located on the 01 Level between the two smokestacks. The small deckhouse just forward of both mounts held the ready service ammunition and, again, ammunition racks would be located on the splinter shields of the surrounding gun tub. The Mk-51 gun directors for the quad 40s were located atop the deckhouse. The gun crew for a quad 40 consisted of eleven men: the pointer, the trainer, the gun captain, and eight loaders.
Prior to the kamikaze hit off of Okinawa in April of 1945, the KIDD held a second set of torpedo tubes at this location. With the diminishing Japanese surface fleet no longer a serious threat and the intense aerial onslaught of the kamikaze squadrons off of Okinawa, the U.S. Navy opted to reduce the torpedo battery on destroyers under repair and mount increased anti-aircraft protection instead. Thus, the KIDD lost her forward torpedo mount but gained two quad 40mm gun mounts while under repairs at Hunter’s Point Naval Shipyard in San Francisco.
A Secondary Conning Station was also added just forward of the aft smokestack along with the quad 40mm gun mounts. This provided the ship with an emergency control station if the bridge was knocked out, as almost occurred during the attack on April 11, 1945. This station was provided with a magnetic compass and sound-powered telephones that connected the men with both enginerooms and the steering gear room. Lookouts could be stationed to either side of the gun tubs nearby to facilitate steering as an operator at the conning station would have his view obstructed by the ship’s superstructure. This arrangement would aid in enabling a severely damaged ship to return to port.
The final twin 40mm gun mount—Mount 45—is located atop the after deckhouse. This mount provided medium range anti-aircraft protection for the aft quarter of the ship. Ammunition was stored in the deckhouse upon which it sits.