Just how good was German Flak

[George Hopp]

In comparison to German flak, here is an example of US AAA from "A radar history of World War II" (page 402): "As an example, in August a bridgehead 40km southeast of Paris was attacked at night by 35 German bombers preceded by three pathfinders and defended by the 109th and 413th AAA Gun Battalions. The attacking planes reached the bridgehead without drawing fire because they responded to IFF interrogation as Allied a/c, disclosing their true identity only after dropping flares. The two battalions brought down all three pathfinders and 13 of the main force with eight probables, and this without proximity fuses."

[Jon]

Thanks for the info regards the US AA.

Interesting as i am reading about the massive battles over Malta, the British and Maltese AA here was also excellent and brought down many Luftwaffe bombers and fighters. Looks to be the more practice (targets) you get obviously the better you will get.
And the Luftwaffe flak arm certainly had many targets.

One further question on Proximity fuses, how close to the target did they have to be for the fuse to detect and detonate?

[JoeB]

Originally Posted by Jon

One further question on Proximity fuses, how close to the target did they have to be for the fuse to detect and detonate?

The VT fuzes of WWII worked on prinicple of doppler shift continuous wave signal. IOW they didn't directly measure the distance to the target like a pulsed radar. The main tuning variable for distance was sensitivity. When the shell got near a target the doppler shifted return signal superimposed on the o outgoing signal would form a "chirp" in the circuit that triggered the fuze. But the reflectivity of the target also mattered.

Empirical tests were used to set the sensitivity. The first generation 5"/38 fuze Mk.32 which entered combat in Jan 1943 had that done by subscale tests. Full scale tests (against various real planes suspended from cables, the B5N "Kate" was mostly used but Allied bomber types were tested too) were done after those fuzes entered service. The typical bursting distance was 70-100' in practice. From "Deadly Fuze" by Baldwin.

The VT fuze raised the effectiveness of USN AA fire an estimated 3 fold in 1943 over time fuzes, later fuzes (similar to the ones used in 3.7" and 90mm AAA in Europe) 4 fold. And USN directors and radars were pretty sophisticated at least equal to German in late war period (so were Army ones), and the main naval weapon a high ROF 5" probably more effective as a basic AA gun than all but the German 128mm, which was rare. And of course the USN had plenty of experience shooting at planes by later war. IOW the best late war Allied heavy AAA was probably several times more effective than German. Had German AAA been as effective it would have been a major problem.

OTOH postwar when evidence of Soviet VT fuzes was detected, very similar to early US ones, a fuze jammer was rapidly developed, likely the same if Germans introduced it, and another ECM/ECCM seesaw would have ensued, though German VT fuzes still would have been bad news without doubt. VT was used against German manned a/c fairly infrequently and late, and their operations research function of detecting new enemy weapons wasn't (obviously) as strong as the Allies, so AFAIK they never realized it. The Japanese had VT fired at them for 2-1/2 years and apparently never realized it.

The Westermann book also points out how very widespread fitting of active jammers to USAAF bombers, though it didn't happen till the fall of 1944, had a big impact on the flak arm, interestingly not so much reducing losses as forcing the Germans to radically increase shell consumption and barrage fire.

Joe

[Jon]

Thanks Joe for the full answer.

So were Shells with proximity fuses still set to detonate at a given altitude but would overide and explode lower if they passed and aircraft.

[JoeB]

Originally Posted by Jon

So were Shells with proximity fuses still set to detonate at a given altitude but would overide and explode lower if they passed and aircraft.

They just had the proximity feature and a self destruct switch: a centrigually operated switch that opened a circuit when the shell started spinning at firing, charging up a capacitor, then closed when the shell's rotation speed decreased sufficiently, discharging the capacitor and detonating the shell. It was factory set according to assumed flight time before the shell got dangerously close to the ground. When VT fuzes were used around Antwerp over populated areas (usually fired out to sea defending England), the switch settings had to be changed at the factory to prevent proximity bursts against the ground when firing at the lower altitude flight profile the V1's adopted at that time. In naval use the fuzes would frequently detonate on sea return if they missed low altitude targets, before the self destruct activated.

A common USN practice was to fire mixed salvo's with some time fuzed shells, even after there were plenty of VT fuzes, to detect gross errors in the fire control solution if the time bursts were visibly far from the target.

Joe

[Jim Oxley]

The details below don't necessarily provide a guide to how effective German Flak was, but it certainly does give a guide to how thick it was.

In June 1944 the Flak regiments located within the borders of Germany deployed 8,876 guns of dreaded 88mm gun; 25,000 pieces of 20mm and 30mm cannon and were manned by 900,000 men.

That was a result of the bombing campaign by the RAF Bomber Command and 2nd Tactical Air Force, and the 8th and 9th USAAF.

To put those figures into perspective Rommel only had 35 x 88mm guns when he attacked the British in the Desert in 1941. The German Army in France only numbered 500,000 men at the time of the Normandy invasion.

[ArtieBob]

The basic WWII USN fire control system was the Mk 1, which was a mechanical analog computer. Solutions were good whether the inputs were from optics or radar and the aircraft true velocity was less than 400 knots. There were several problems, optical data on angular position could be very accurate, but optical ranging, particularly with a fast moving target was not as precise. Early radars because of the wavelength and lobe dimensions was sort of the opposite, more accurate in range, less accurate for angular position. So the best inputs were to use optical angular tracking if conditions permitted and radar ranging. But even with radar ranging, the margin for error in fuse setting is great because on a 5”/38 mount the fuse is set before the round is manually loaded. On the standard 5”/38 dual mount, this is done in the shell elevator which brings the projectile up from the lower handling room. If I remember correctly, the maximum firing rate for the twin mount is something less than 20 rounds per minute, or a cycle time of about 6 seconds per gun reloading, add to this the time in the elevator and the time of flight and you will end up with a 15 to 20 second lag between the setting of the fuse and detonation. If the target is manuevering, a time error of .1second would probably render the shell ineffective. If you have ever had the chance to see the movies of kamikaze attacks during WWII, the sky is obliterated by overlapping AA bursts, yet the aircraft just keep coming. The VT fuse eliminated the timing errors. IIRC in my gunnery classes, the USN felt the effectiveness was increased by a factor of 5.

Best regards

Artie Bob (ex-second loader 5”/38 mount (lower handling room)