Harold Crawford says "A 40 MM gun that I used to be on, when I was in the AAA units back in the 50s." No disrespect, but bet that if the aircraft was flying more than 3,000 feet away, the gunner's ears were more at risk than the aircraft :-| Just look at those iron sights!! Bet they couldn't track/hit a Piper Cub flying half a mile away!
	This is the 770th AAAGBn with 120 mm (almost 5 inch diameter) anti-aircraft guns at firing practice at Yakima Firing Center, ca. 1952. [There should be an M-33 radar/gun-director somewhere, I guess off camera.]Courtesy Al Miles via Mark Morgan

Most Aircraft Reached their Targets in World War II

During the 1942 Japanese conquest of Manila in the Philippines, the Japanese planes simply flew higher than the maximum vertical range of the United States anti-aircraft guns. Many people felt that since the guns had no effective pointing system against aircraft targets, the Japanese planes could have flown anywhere quite safely. Also see a Pearl Harbor story

This anti-aircraft situation was typical. Ground fire against aircraft looked impressive, but downed few planes. Fighter planes were more effective, but even with combined fighter planes and anti-aircraft guns, most bombers (German, British, American, Japanese) reached assigned targets and dropped their bombs.

In most air raids (by either side) more than 90 percent of the bombers returned to safe airports. Air crews probably felt that a 10 percent loss was very high - but defenders took a pounding. Down town London was mostly gutted - most large German cities were heavily damaged - most Japanese cities were heavily damaged before the atom bomb really did the convincing.

Author gets flack. Several people felt the above is not strictly true. They point to the very successful air defense of the Normandy landing areas in June of 1944. The Allies put/kept all their available fighter planes over the Normandy beach heads. One report says that 11,000 Allied aircraft were involved with the Normandy invasion. Yes, there were few reports of German aircraft. One British fighter wing history reports that the Germans mounted about 100 sorties, but does not mention combat with them. Allied ground and naval forces were not bothered enough by German aircraft to write anything about them in the battle summaries. One can still claim that the threat of anti-aircraft fire was not what kept the Germans away. I propose that German command confusion (Hitler) and 11,000 Allied aircraft kept most of the German aircraft away from the Normandy invasion.

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The V1 - 1st Cruise Missile

Image stolen from page Fi-103/V-1 "Buzz Bomb" of Warbirds Resource Group - permission has been asked - I don't suggest this method of business, but I just hate it when good stuff disappears from the Internet.

On June 13, 1944, Germany started firing V-1 aircraft into London. The V1 'buzz bomb' was the first cruise missile. It was a low flying (300-3000 ft.) fast for its day, (360-400 mph) un-piloted aircraft with a warhead of almost one ton. During the next 9 months, about 8000 were fired against London (and another 6000 against other targets in Allied held Europe). The V1s killed about 2000 people in London, wounded about 25,000 and did serious damage. (The damage and casualties would have been higher if the British had not fooled the Germans into setting the target range of the V1s a little short.)

Getting ready for the V1 attack
In 1943, Allied photo reconnaissance spotted German V1 development efforts, and the British took the threat very seriously. In 1943, the British anti-aircraft czar General Frederick Pile ordered a large number of fire control computer ("predictor") systems from Bell Telephone. (During World War II, the Bell Telephone company (and Western Electric, its manufacturing arm) had designed and manufactured several anti-aircraft fire control systems for anti-aircraft guns.) Nine months later (June 1944, just in time for the German V1 attack) the "predictor" systems were being installed in England. (How is that for quick turn around?).
(General Sir Frederick Pile later wrote the book "Ack-Ack: Britain's Defence against Air Attack during the Second World War", available on the British used book market. I have not seen the book as of late 2002.)

Some fun information about the SCR-584 from http://www.project1947.com/roswell/radar.htm

- Data from U.S. War Department Technical Manuals TM11-1324 and TM11-1524 (published April, 1946 by the United States Government Printing Office) Wavelength 10 cm Frequency (four bands around 3,000 MHz) Magnetron 2J32 Peak Power Output 250 kW Pulse Width 0.8 microsecond Pulse Repetition Frequency 1707 pulses per second Antenna Diameter 6 feet Beam width to half power 4 degrees Maximum Range PPI Search 70,000 yards (39.7 statute miles) Auto-Track 32,000 yards (18.2 statute miles) Potentiometer Data (artillery control) 28,000 yards (15.9 statute miles) Minimum Range 500 - 1000 yards Lower Elevation Limit -175 mils (-9.8 degrees) Upper Elevation Limit +1,580 mils (+88.9 degrees) Azimuth Coverage 360 degrees Azimuthal scan rate in search mode 5 revolutions per minute Range Error 25 yards Azimuth Error 1 mil (0.06 degree) Elevation Accuracy 1 mil (0.06 degree) Power Requirements 115 V, 60 Hz, 3 phase, 10 kVA maximum (without IFF)

(James Burke in "Connections" and Robert Buderi in "The Invention That Changed the World" called the predictor "Number 9". Nick Spalding has the training schematics for "PREDICTOR AA No. 10".)

Burke said "Devilish difficult things to hit, buzz bombs. At first it took the antiaircraft gunners 2500 rounds to bring one down. Then (and on behalf of the U.K., I thank you Bell Labs), along came the M-9 Predictor, and the cost of bagging the doodle bug went down to 100 shells. Significant savings all round (including lives). All it took was the magic math to run a feedback loop that could update constantly the set of data you got from the radar about the incoming buzz bomb's last position, so as to be able to make a good guess at its next and to point the guns that way. Then boom."

Nick Spalding says

"In its original 1944 incarnation, shooting down V1s, the radar was not a tracking radar - it only gave range. Tracking was accomplished by an optical tracker, essentially a large double theodolite with a seat of either side with one operator following the bearing and the other in elevation. The output of that was taken by magslips (later known as synchros) to the predictor, AND to the radar to point it in the right direction. At the time I encountered it in 1955 it was fed from the British 4 Mk 7 radar which was a true tracking radar which sent and received via a single dish. There were a couple of what I think were SCR584s around the equipment park which had separate dishes for send and receive." (Some of the sin and cosine potentiometers used to convert radar range and pointing information to x, y and z coordinates were 3 feet in diameter. The operational amplifiers had to be hand zeroed every few minutes.) The British used 3.7 inch (90 millimeter) and 4.5 inch (110 millimeter) anti-aircraft guns at this time."

William Donzelli comments on the first paragraph above:

The radars that he is referring to were SCR-547s. These were the "Mickey Mouse" radars from Western Electric, and could manually track a target and furnish azimuth, elevation, and range data to the director. It could also optically track as well, being fitted with some telescopes.

David H. Ternes points out that

"this section does not mention the use of the VT fuze (variable time or proximity fuze) for anti-aircraft guns. These fuzes came into use by the U.S. Navy in 1943, and were employed in Great Britain by 1944. They gave the defending anti-aircraft gunners a major advantage, since when using a VT fuze it was not necessary to correctly estimate the time of flight to intercept an enemy aircraft. The relatively high kill rate for U.S. Navy anti-aircraft guns as compared to Imperial Japanese Navy anti-aircraft guns attests to the success of the fuze. The fuze was used as part of the defense against V1 attacks against Great Britain. While not the only factor in the success of the British anti-aircraft guns against the buzz bombs, the VT fuze was a notable contributor."

Very true. (See The Radio Proximity Fuze - A survey.) The artillery shell in general does not impact the airplane, however, if you can get the shell to pass near the plane, and if you can explode the shell as it passes near the airplane, you can likely do serious damage. Before the VT fuse, the gun crew adjusted a timer on the fuse of the shell just before inserting the shell into the gun. Determining the correct setting of the fuse, had been one of the major problems of anti-aircraft gunnery.

Since the shell is traveling about 1/2 mile per second, trying to get the shell to explode within say 30 feet of the airplane requires the shell to explode plus or minus 0.015 seconds of optimum. If the plane is at 20,000 feet, the flight time is about 9 seconds. The percent error in the time must be less than 0.15 percent, an interesting challenge of fuse timer design and construction if nothing else.

Using radar ranging, radar or optical sighting for azimuth and elevation, and a computer generated better gun pointing. Part of the gun pointing problem is determining how long (in seconds) the shell must fly to the predicted intercept point. This flight time became more accurate - but - the prediction was valid for right now. If the fuse setter set this time into the shell, handed the shell to the loader, the loader loaded, closed the breach block, etc. up to 7 seconds had passed - and a new flight time is more valid. So the computers were modified to provide a time value that would be as good as possible say 7 seconds from now - and gunners tried to arange their activities so that shell would be fired precisely 7 seconds after the fuse setter did his job. As you can see - there are even more variables and more uncertainties than first apparent.

This whole difficult problem was by-passed with the arrival of sufficient numbers of the efficient VT fuzes. The whole art and science of fuze setting became obsolete.

Fortunately the V-1 was a nice well behaved target, flying low and straight. Actually an almost ideal target. Smarter targets flew higher and continually changed course a little (except during bombing runs).

Jerrry L Brewer Richardson, Texas writes:

I was in B-238th AAA 90mm in Japan during the Korean War. I went to Far East Anti Aircraft Specialist School In Hyoshi Japan and they just danced around the topic you covered. There are some more problems that enter the equation that make it worse: weather, powder temp, different ammo batches, barrel life of the individual weapons, dead time from time the fuse is cut till ignition,and so on. Our SCR-584 only had one antenna and we were on full radar nearly all the time. We never had any daytime alerts. On page three you refer to an optical tracker. Can you remember the military nomenclature for this device. I am writing a picture history of my two years in AAAand I am hung up on this item.

The V1 attack and British Defense
The V1 attack had 3 main phases
- June to September 1944 (main attack - Germans had launching sites in range)
- July 1944 to January 1945 (Heinkel 111 aircraft launched V1s from over North Sea)
- March 3 to March 31 1945 (150 of a longer range version V1, only 13 got through!)

Final defensive score card for defending London against the V1

New Zealand Fighter Pilots Museum says that in many successful V1 intercepts by aircraft (fighter planes), the 1 ton bomb exploded providing great danger to the pilot. The New Zealand 486th squadron lost 17 Tempest planes and 3 pilots in these blasts.

The V1s were relatively easy targets, yet 25 percent of V1s got through to London

'Easy' because:

- Fighter planes had already shot down some over the English channel

- Low altitude (range) gave the guns shorter time of flight, therefore higher accuracy,

- Low straight flight made it easy to predict a point of intercept,

- V1s used no electronic counter measures (jamming, chaff).

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German Efforts against Allied Bombers

The Germans fighters and anti-aircraft guns had a much lower success rate against Allied bombers. Allied bombers flew high (15 to 20 thousand feet) to evade the guns and in large formations (often referred to as bomber streams) to help defend against German fighters. The Germans gunners only had to set the fuses to explode at the altitude of the stream and shoot up into the 'stream', and their success was very limited. German officials recognized the ineffectiveness, but kept up the attempt to cheer up the German civilians. The guns were most dangerous (moderate) when Allied aircraft were flying straight during bomb runs.

Life takes strange turns. A classmate of mine in Nike anti-aircraft school (1954) was a new U.S. citizen. His previous citizenship had been German. When he had been 14, he had loaded German anti-aircraft guns - firing at United States bombers over Germany.

The number of large anti-aircraft guns used to defend German cites against Allied bombers is quoted as 18,000. One commentator states that the Germans probably lost the Battle of Stalingrad by defending German skies against Allied bombers

Even against the combination of German fighters (some days 600 were available) and numerous anti-aircraft guns , usually 95 percent of the bombers dropped their bombs on or near their assigned targets and returned in re-usable condition to England. (Very few Allied raids had bomber losses higher than 20 percent. "Terrible losses" as viewed by bomber air crews, and "not nearly enough losses" as viewed by the Germans.)

Comments from Jerry L Brewer who did U.S. 90 mm AAA in Japan during the Korean police action.

One final thought on AA guns against modern aircraft. It was taking your faithful old shotgun out to shoot birds flying by at 100 MPH. German author Werner Muller in his book "The Heavy Flak Guns" said,"Based on average monthly ammunition consumption in 1944, it took 16,000 rounds of 88mm gunfire to bring down one four engine bomber." Mr. Mullers book contains details on German AA guns and fire control systems. It is published by Schiffer Publishing Ltd. of Westchester Pa.ISBN: 0-8870-263-1 Available by e-mail through Barnes & Noble I am sure that one Nike rocket was a better buy than 16,000 rounds of 90mm ammo.

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