AAA Umbrella vs Rain of Bombs
Naval Anti-Aircraft vs Aircraft in World War II
“Nothing can stop the attack of aircraft except other aircraft” – William “Billy” Mitchel
Before World War II, air power enthusiasts believed air power would sweep the seas clear of ships and dominate war on land as well. Dramatic events like Pearl Harbor helped convince others that the day of the battleship, and perhaps surface ships, was over. However, an analysis of WW II anti-aircraft and ship damage by aircraft shows ships, especially battleships, were able to defend themselves effectively, even in the absence of their own fighter cover.
The Threat:
Aircraft presented a new challenge to naval tactics and operations. Scouting, previously done by smaller warships, could now cover larger areas at faster speeds via aircraft. When radios and radars were developed, this further expanded the intelligence, surveillance and reconnaissance (ISR) capabilities of naval forces supported by aircraft, either land or ship based. On the attack, aircraft presented a new threat akin to torpedo boats which had challenged naval orthodoxy in the late 1800s. Like a torpedo boat, aircraft could deliver torpedoes which presented mortal threats to even capital ships. The defense against such attacks was similar to those against torpedo boats: rapid firing cannon to dissuade or destroy attackers before they released their weapons, and screening vessels to make it more difficult to approach the primary target. Unlike torpedo boats, aircraft could also deliver bombs to strike the decks of ships from high angles. For ships, bombs delivered by dive bombers or from level flight which scored near misses were also dangerous since they could rupture hull plates and damage the ship via shock. This was proven in the tests against KMS Ostfriesland in 1921 and in the wartime sinking of IJN Akagi at Midway, and in many other examples.
At the start of the war, U.S. and British forces were most concerned with dive bomber attacks. The reasons were twofold. One, anti-aircraft artillery (AAA) technology made it difficult to track and engage these fast, steeply diving targets. Two, dive bombing was more likely to hit the target than torpedoes. While high altitude level bombing was possible, in wartime the hit rate against maneuvering ships at sea was negligible. The U.S. Navy’s own prewar studies had determined the success rate of horizontal attacks against capital ships at sea was near 8%. Japanese carrier based level bombers achieved a 16% hit rate against the stationary battleships at Pearl Harbor. However, against maneuvering targets at sea it was close to 0%. In World War II, only one warship at sea was sunk by horizontal bombing, a Japanese destroyer that believed the attacking B-17s were so ineffective it took no evasive action. The USN also made unrealistic damage predictions in its prewar games and exercises. Battleships were harder to kill with airpower, compared to prewar predictions, and every other class of warship far easier to kill. This was especially true for the carriers, which had been rated as durable as battleships against bombs in exercises but were found to be far less resilient to bomb damage in reality.
The Wartime Results:
It is easy to find dramatic events that support the idea that airpower was very effective against ships in WW II: the carrier air raids on Pearl Harbor and Taranto, each sinking and crippling multiple battleships; the land based air sinking of HMS Prince of Wales and HMS Repulse; the carrier air sinking of IJN Yamato and IJN Musashi; the sinking of KGM Tirpitz by heavy bombers; KGM Bismarck’s crippling by an air dropped torpedo that allowed a vengeful British fleet to catch her. However, for each of these events, there are counter examples or considerable mitigating factors.
Sinking ships at a pier in port during a surprise attack and using this as evidence of its wartime utility is like judging an air force fighter’s capabilities when destroyed on the ground. Additionally, surprise attacks like Pearl Harbor and Taranto are almost always very effective. Hitting someone who isn’t prepared is a great military tactic and much easier to accomplish. However, when effective defenses were employed, results were different. During the eight month siege of Tobruk, 4,105 enemy aircraft were engaged by harbor and ship AAA. Only seven ships were sunk in the harbor for 374 aircraft losses. The harbor remained in operation. KGM Tirpitz in her fortified fjord was attacked by 521 bombers with hundreds of additional support aircraft over months before succumbing. Prior to her sinking by very heavy bombs from a massed flight of level bombers, only one attack had inflicted any significant damage on her from the air. Her deck armor was proof against dive bombing. During the British surface attack against Mers-el-Kebir, the French battleship Strasbourg got underway and escaped the harbor. She shrugged off a carrier aircraft attack, downing two aerial adversaries while sustaining no damage.
HMS Prince of Wales and HMS Repulse did succumb to air attack at sea, the first battleship and battlecruiser to do so. However, the hit rate against them is telling. At Pearl Harbor, 43% of the torpedoes launched hit their stationary, surprised targets. Off Malaysia a few days later, only 16% of the torpedoes found their target. Repulse dodged 14 torpedoes before being struck and slowed, allowing three more hits to finish her off. Prince of Wales suffered an early hit that doomed her, like Bismark. Not only did it reduce her speed, but it knocked out the electrical generation her AAA depended on. This left her far more vulnerable to the follow-on waves. These ships were also devoid of any additional escorts to contribute to anti-aircraft artillery (AAA) fire. U.S. post war analysis showed that 60% of aircraft were shot down by screening ships rather than the targets. Had these vessels had escorts or AAA systems that did not rely on the ship’s power, they might have fared better.
A single torpedo hit to KGM Bismark crippled her maneuverability and doomed her to destruction by the pursuing British fleet. But, like the Prince of Wales and Repulse, she had no escorts. She was also finished off by heavy guns and torpedoes from the British fleet, not with airpower. In an opposite case, an 8” hit on IJN Hiei off Guadalcanal left her unmanuverable. When dawn came, waves of U.S. aircraft, including B-17 level bombers achieving a 2% hit rate, eventually finished her. Here, aircraft definitely facilitated the death of a capital ship, but were not the sole causal factor.
In other examples, the Italian battleship Vittorio Veneto weathered an air attack during the Battle of Cape Spartivento with no damage. During the battle of Cape Matapan, she took an air dropped torpedo hit to her stern inflicting damage eerily like what Bismark would sustain two months later; but unlike Bismark, she was able to recover from the damage and escape pursuing British surface forces. Her escorts, which stayed behind to protect a crippled cruiser, did not survive their encounter with the British battleships. Before the famous torpedo attack on Bismark, the same aircraft attacked HMS Sheffield in a case of mistaken identity but achieved no hits. She defended herself with maneuver alone. In March 1942, Bismark’s sister ship KGM Tirpitz was attacked at sea by 20 carrier based torpedo bombers and emerged unscathed. During the Battle of Empress Augusta Bay, four CL and four DD were attacked by 100 Japanese aircraft. They took two bomb hits that only inflicted minor damage, and shot down 17 of the attackers. Much earlier in the war, one heavy and three light cruisers with four old destroyers, none with modern AAA fittings, shot down 6 of their 36 attackers (16%) with one cruiser disabled. Had the formation stayed together, rather than scattering for maneuverability (proven to be better tactic based on wartime experience) they might have emerged unscathed. The HMS Ark Royal, attacked on 26 September 1939 by German aircraft, struck her own fighters below deck, fighting them off with AAA alone. On two occasions IJN Ise came under attack by nearly 100 US carrier based aircraft and escaped. This totals more aircraft than the IJN sent to bomb Battleship Row in Pearl Harbor.
The Pedestal Convoy to Malta in 1942 also showed the ability of ships to persevere in the face of determined air attack. On 11-12 August, over 163 aircraft attacked the convoy which included two carriers. The carrier fighters were only credited with eight attacking aircraft and several of the reconnaissance aircraft shadowing the force. The defending flak accounted for a similar number, but was intense enough to dissuade most of the attackers from pressing home their attacks. It wasn’t until the force came within range of German Stuka dive bombers that hits began to mount, but for 220 escorted bomber sorties only two ships were directly hit, and one forced to leave the convoy due to damage from a near miss. On 13 August 1942, an additional 78 aircraft made a highly coordinated attack against the convoy whose escorts had been thinned out, and inflicted no damage. While there was some carrier based and land based air cover for the convoy, the number of fighters relative to attackers was very small and lack of IFF complicated fighter direction in defense of the convoy. The vast majority of the attackers made it within AAA range and were turned back by ship defenses, a case that contradicts Billy Mitchel’s opinion. It was only near the end with ammunition dwindling and escorts thinned that air began to strike home, but still failed to stop the convoy.
The fate of the Japanese Center Force at Leyte is yet another example. Hundreds of aircraft sorties were directed against her by US carriers, all in good weather with negligible fighter opposition. Japanese AAA was limited by ammunition expenditures. While the super-battleship Musashi was sunk, the Center Force continued on its mission to engage the US fleet. Airpower did not stop it. While some point to the lack of fighter cover as a critical failure of the Japanese, their tactics rationing AAA expenditures also severely hampered their effectiveness. Killing a single battleship with all these advantages is not a testament to the ability of airpower to stop ships.
In addition to the historic anecdotes above, there is wartime data on the effectiveness of anti-aircraft in dissuading and destroying attackers. British post war analysis showed that defensive fire reduced the chance of any ship being hit by 50%. Additionally, ships that fired AAA were far less likely to suffer fatal damage. For the United States Navy, 1394 attacking aircraft were shot down by defending fighters. That can be seen as very good, but about 7600 attacking aircraft made it to AAA range of warships. This means only about 15% were killed before reaching the fleet, although more were probably scattered or prevented from continuing. Of those that arrived within AAA range of the USN, 2256 were shot down by AAA, or about 30%. Ships gunnery killed more attackers than defending fighters did, and was twice as effective by percentage of kills. Billy Mitchel was wrong. Aircraft could be stopped without aircraft. Japanese AAA fire was less effective in achieving kills, but still could prevent hits as noted above. During the Marianas carrier duel, only 3% of US attacking aircraft were lost to IJN AAA, compared to 32% of the IJN aircraft to USN AAA. However, part of this can be traced to Japanese tactics limiting ammo expenditures vs AAA targets due to low supplies of ammunition. Japanese tactics required ceasing fire before shooting 20-25% of what USN data showed were average rounds expended per kill. The USN also had more sophisticated AAA fire control and proximity fuses to increase its effectiveness.
Battleships vs Aircraft:
One specific class of vessels did surprisingly well against attacking aircraft when it was underway and defending itself: battleships. The section above gives several examples of battleships successfully beating back aircraft attacks. As the U.S. Navy’s own analysis states, battleships “shot down twice as many [kamikaze] planes as would have been expected on the basis of their opening ranges, the amount of ammunition they fired, and the average success attained by all ships under similar conditions.” When parsing the data and normalizing for the larger AAA battery a battleship carried, it was a superior AAA platform. The stability of a larger, heavier base is probably one factor, but it should also be remembered that a BB was less able to employ all of its AAA weapons than a DD or CL, since the smaller ships had larger fields of fire for their centerline weapons as opposed to a BB which had many crowded on port or starboard and was thus unable to engage to the opposite side. Besides basic stability, it is also possible that battleships relied less on maneuvering to dodge attacks. Not maneuvering as violently would also have increased AAA effectiveness at the heighted risk of being hit.
Being hit was less of a concern for a battleship than other vessels due to armor. Carriers, even armored ones, were extremely vulnerable to dive bombers plunging bombs into their innards. Destroyers and cruisers could normally rely on their maneuverability, but dive bombing to low pull out altitudes negated many defensive maneuvers. Battleships had deck armor to resist plunging fire of high caliber and velocity gun rounds. Dive bombers would release their up to 1000lb weapons at below 2000ft to hit their targets more accurately. This would impart striking velocities greater than 200mps. While impressive, this was half the velocity and less mass than a 14” battleship round at range. Pre-treaty battleship deck armor, designed to resist plunging fire, could negate these hits. Older battleships, with 2-3 inches of deck armor, could resist 1000lb projectiles unless dropped from over 4000ft, where accuracy greatly suffered. Modern WW II battleships had thicker deck armor, being immune to 1000lb projectiles from any operational height and 2000lb AP bombs from any height below 7000ft. For perspective, the 1,757lb AP bomb that sank Arizona was dropped from about 10,000ft against a stationary target. The only aircraft a battleship truly had to fear were torpedo bombers, and even then multiple hits were needed. If screened by escorts, multiple large waves of aircraft were needed to achieve this, and it was only accomplished twice, late in the war against formations with limited AAA ammunition.
Conclusion:
As shown above, ships in WW II were very capable of defending themselves from air attack if they had room to maneuver and the weapons and ammunition available. This is not to say aircraft played no role. Indeed, even a small defensive fighter presence could disrupt an incoming attack, preventing it from coordinating, and drive some aircraft off before they began their attack runs. Air attack did sink more warships than submarines or surface actions, and almost as many as both combined. However, air power did not dominate war at sea any more than it dominated war on land. Warships were able to fight and continue their missions despite massive air attacks, and independently of their own air cover. I t did not take an aircraft to stop an aircraft. A determined AAA battery could, and did, do it as well.
CDR Patton is deputy chairman for the U.S. Naval War College’s Strategic and Operational Research (SORD) Department. SORD produces innovative strategic research and analysis for the U.S. Navy, the Department of Defense, and the broader national security community. CDR Patton was commissioned in 1995 from Tufts University NROTC, with degrees in history and political science and has served four tours conducting airborne nuclear command and control missions aboard the US Navy E-6B Mercury aircraft, and two tours as Tactical Action Officer (TAO) and Combat Direction Center Officer (CDCO) aboard the carriers USS KITTY HAWK and USS NIMITZ. He has two Masters Degrees from the U.S. Naval War College.
His opinions are his own and do not necessarily represent those of the Department of Defense, U.S. Navy, or the U.S. Naval War College .
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