defoliate trees from the point of impact. The final type of ammunition developed for the 16-inch guns, well after the Montanas had been cancelled, were W23 "Katie" shells. These were born from the nuclear deterrence that had begun to shape the US armed forces at the start of the Cold War. To compete with the United States Air Force and the United States Army, which had developed nuclear bombs and nuclear shells for use on the battlefield, the Navy began a top-secret program to develop Mk. 23 nuclear naval shells with an estimated yield of 15 to 20 kilotons. The shells entered development around 1953, and were reportedly ready by 1956; however, only the Iowa-class battleships could have fired them. Secondary battery The secondary armament for Montana and her sisters was to be twenty /54 cal guns housed in ten turrets along the superstructure island of the battleship: five on the starboard side and five on the port. These guns, designed specifically for the Montanas, were to be the replacement for the /38 cal secondary gun batteries then in widespread use with the US Navy. The 5-inch/54 cal gun turrets were similar to the 5-inch/38 cal gun mounts in that they were equally adept in an anti-aircraft role and for damaging smaller ships, but differed in that they weighed more and fired heavier rounds of ammunition at greater velocities, thus increasing their effectiveness. However, the heavier rounds resulted in faster crew fatigue than the 5-inch/38 cal guns. The ammunition storage for the 5-inch/54 cal gun was 500 rounds per turret, and the guns could fire at targets nearly away at a 45° angle. At an 85° angle, the guns could hit an aerial target at over . The cancellation of the Montana-class battleships in 1943 pushed back the combat debut of the 5-inch/54 cal guns to 1945, when they were used aboard the US Navy's s. The guns proved adequate for the carrier's air defense, but they were gradually phased out of use by the carrier fleet because of their weight. (Rather than having the carrier defend itself by gunnery, this would be assigned to other surrounding ships within a carrier battle group.) Anti-aircraft batteries While the Montana class was not designed principally for escorting the fast carrier task forces, they would have nonetheless been equipped with a wide array of anti-aircraft guns to protect themselves and other ships (principally