eli5 Anti-Aircraft guns. WW1/WW2 era

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How did soldiers control the altitude at which anti-aircraft ammunition (flak) detonated? How could they know if the flak rounds would go off at 5000 feet, 10,000 feet etc? Were they magnetized somehow to detonate near aircraft? First post. Please be kind. Lol.

In: Engineering

Most flak rounds operated on fuse so the detonated at those cause that’s what the fuse was set hince why some round detonated early and late not really much more too it really

Early shells were detonated by a simple timer. Slight changes to the time meant explosions at different heights. Flak was a random shot in the dark, not very efficient.

During WW2 the British developed a rugged vacuum tube that could be used to make tiny radio transmitter/receiver. When close to metal aircraft, the radio signal would be reflected back to the receiver, triggering the explosion. This was the first proximity fuze.

Bursting AA shells were time-fused. You did the math to figure out how long it would take the shell to get to a certain altitude, and then set the fuse.

Later in WW2 radar-fused shells were developed by the US that used a radar in the nose of the shell to detect nearby aircraft.

The German flak could be adjusted with a shell timer. A flak spotter would call out if the flack was exploding too soon or too late. Once they had it dialed in, it could be withering.

Especially to flights of bombers who are flying at similar elevations. Also, they were in formation, which made them easy targets.

In the early runs of the eight Air Force bombing germany, on a single mission it was not uncommon to lose 30% of the bombers and crew..

Once they figured out the timer setting on the shell, this info was communicated to other flak batteries along the flight route of the bombing run.

Most shells were time based, you know the speed of the round when it leaves the gun and the distance to the target so the timing is relatively straightforward. A lot of gun systems would automatically set the time on the fuse based off the target that was being followed. There was some variability in the accuracy of the fuse but when they’re throwing up a lot of rounds it actually helps to make a scary cloud that isn’t easy to just fly over because they’re off by a bit.

Later in the war the US started using the AAVT round in their 5″ guns on ships which used some cheats with antennas and receivers to detect when a plane was ahead of it and relatively close and then detonates to hit them with the cloud of shrapnel rather than needing to physically hit the plane which is pretty hard to do. There was also a 90mm version that was used to snipe V1 bombs which moved a lot faster than a standard plane of the era

Early shells had timed fuses. Artillerymen were trained on how to estimate the height of aircraft and how to adjust the timer so that the shell would detonate at *around* that same height, depending on the type of shell and the firing angle. That’s fairly simple math: shell goes at X feet per second, you need it to explode at Y feet, so you set the fuse to Z seconds.

Of course, it’s *not* that simple since the shells aren’t going straight up, they’re fired at an angle. So there’s some trigonometry in there if you were to sit down and do it “right”. They didn’t have that kind of time so they just made estimates, fired a shell, paid attention to where it went off (and how close it was to the altitude of the planes they were shooting at) and adjusted the timer on the next shell accordingly. For the most part, though, the strategy was to fire an ass-ton of flak shells and hope that at least a few of them exploded at the right altitude and close enough to a plane for the shrapnel to be dangerous, and then hope that some of that dangerous shrapnel did its job.

The other problem was that those timers weren’t super reliable. WWI timing fuses were made from something that burned at a fairly predictable rate, like [a stereotypical string fuse](https://www.youtube.com/watch?v=oq8jzn2sd-g). The problem is that those don’t always burn at exactly the same rate, especially at different altitudes. By WWII most shells were using clockwork fuses, which greatly increased the accuracy.

In 1942 British engineers figured out how to use reflected radio waves in the shell to create proximity fuses that would explode when the *shell* knew it was close enough to a plane. They still weren’t perfect and sometimes exploded early or late, but they were leaps and bounds better than timed fuses. The British military actually restricted their use to the navy for a long time so that if a shell failed to explode it would disappear into the ocean where the Germans couldn’t find it to figure out how exactly the British were suddenly way better at shooting down planes.