Antiaircraft refers to surface-to-air weapons systems. During the Second World War, these were almost exclusively guns of various kinds, although barrage balloons saw some use and the Japanese equipped their ships with antiaircraft rockets late in the war.
Antiaircraft guns are divided into light and heavy categories, and sometimes the lighter guns are classified as light and medium. Heavy antiaircraft guns fired large shells to high altitudes, with the detonation timed to destroy the enemy aircraft with a rain of shrapnel. The Allies revolutionized heavy antiaircraft artillery with radar direction of the guns and by adding a tiny radar fuse to the shell itself. This set off the shell when it passed close to an aircraft. These VT shells were three times as effective as ordinary timed shells in spite of a high dud rate.
Light antiaircraft guns were designed to hit aircraft at shorter ranges and traded weight of shell for rapid traverse. The lightest guns in use at the start of the war were large-caliber machine guns firing a solid shot, which proved almost useless. Later light antiaircraft guns fired contact-fused explosive shells. Like solid shot, these had to actually hit the target to damage it, but they packed much more punch.
Medium antiaircraft guns were guns of around 40mm caliber that otherwise resembled light antiaircraft guns. One might anticipate that these would combine the worst features of light and heavy antiaircraft guns, but in fact the 40mm Bofors used by the Allies was quite successful, especially against the kamikazes.
The best heavy antiaircraft naval gun of the war was the U.S. 5”/38 dual-purpose gun, which was often radar-directed and fired VT shells. The best Japanese heavy antiaircraft naval gun was the 3.9”/65 dual-purpose gun, but this was neither as effective as the 5"/38 nor available in adequate numbers. The best medium gun was probably the Bofors, while the Allies relied on the 20mm Oerlikon for light antiaircraft duty. The Japanese had only their dismal 25mm/76 antiaircraft gun.
Unguided antiaircraft rockets were largely unsuccessful. The antiaircraft rockets that the Japanese added to their surface ships apparently did not shoot down a single Allied aircraft.
The numbers of antiaircraft guns shipped at the start of the war proved grossly inadequate. As it became increasingly clear that ships were highly vulnerable to air attack, both the number and quality of light and medium antiaircraft guns was increased. U.S. ships that reported to a yard for repair or overhaul usually shipped additional antiaircraft guns. The Japanese also added large numbers of light antiaircraft guns to their ships as the war progressed, but these were generally not as effective as American weapons. Further gains in antiaircraft firepower were achieved by adding more and better directors for the guns. The ultimate limit on how many guns could be shipped was determined by a combination of deck space; maximum allowable top weight; and, on heavier warships such as battleships, the need to leave clear fire arcs for the main armament. For example, Yamato required special antiaircraft gun mounts to withstand the terrific blast of its 18.1" main armament, but by the end of the war, the Japanese were crowding her deck with additional antiaircraft guns whose ability to survive beyond the first broadside was questionable.
The rapid growth in antiaircraft armament strained logistics. For example, on 11
November 1943, a raid by about 110 Japanese aircraft engaged an
American carrier group that had just conducted a raid on Rabaul. During the 46 minutes of the
battle, the three carriers in the group expended 748 rounds of 5"
ammunition, 8747 rounds of 40mm ammunition, and an incredible 33,552
rounds of 20mm ammunition.
The American fleet had
an impressive service force for keeping up with demand, but the
Japanese encountered serious difficulties in this area. Japanese staff
officers interviewed after the war told American historians that the Yokosuka, Kure, and Sasebo
munitions depots were completely emptied of 25mm ammunition when
Japanese ship magazines were fully loaded out for the impending
conflict. By 1944, ammunition loadouts were restricted to about 100
rounds per heavy antiaircraft gun and 1000 rounds per antiaircraft
machine gun. This corresponded to about 17 minutes of rapid fire from
the heavy guns and just 10 minutes for the light guns. The consequences
for Japanese air defense against repeated American air strikes seems
obvious.
The threat of air attack also led to modified fleet tactics. The Americans quickly adopted a circular formation for task forces that maximized the effectiveness of their antiaircraft batteries, and the Japanese followed suit. As American fleets grew larger, fire control doctrines were worked out to ensure that ships were able to concentrate their fire without hitting friendly aircraft or each other. By 1944, the combination of Hellcats and improved antiaircraft made American task forces all but impregnable to conventional air attack.
Kamikaze attack was another matter. A kamikaze attack could be repelled only by so severely damaging the aircraft that it was forced off its attack trajectory. The Oerlikon proved inadequate for this task, and even the Bofors did not always disintegrate the aircraft in time. The U.S. Navy began developing a 3" antiaircraft gun with an autoloader giving it a rate of fire of 50 rounds per minute, but the war mercifully ended before it went into production.
One fleet tactic devised to counter the kamikazes was the picket destroyer with local fighter CAP. A single destroyer with modern radar was stationed along a likely threat axis at some distance from the main fleet, and two or more fighters were assigned to fly continuous patrol over the ship. In theory, the destroyer gave early warning of incoming raids and the fighters protected the destroyer. In practice, the early warning proved highly useful, but the incoming kamikazes tended to attack the picket destroyer rather than the more valuable targets beyond, and the fighter cover and the destroyer's own antiaircraft defenses often proved inadequate. As a result, picket destroyers took terrible casualties, and there were clear indications of declining morale among destroyer crews during the Okinawa kamikaze battle.
Browning machine gun (typical naval machine gun)
References
CombinedFleet.com
(accessed 2007-7-24)
The Pacific War Online Encyclopedia (c) 2006 by Kent G. Budge. Index