Bomber Armor In WW2

I saw a fascinating video on Youtube the other day. The USAAF was concerned about the heavy losses its bombers were experiencing during daylight missions in the ETO. They collected data on all the damage B-17's had experienced during their missions, consisting of a chart for each damaged bomber that marked where the hits were on a diagram. A group of experts at Columbia University analyzed the data and found that the fuselage absorbed the largest percentage of hits, followed by the wings. The engines and cockpit area had the lowest percentage of hits, at about 1% to 3%.

The USAAF had determined that up to about 1500 lb of armor could be added to the B-17 without affecting performance too badly. It was pretty obvious to everyone that the areas where the most hits had occurred should receive the most armor.

But then a mathematician at Columbia, Abraham Wald, announced they were doing it completely wrong. They were trying to figure out where to put the armor by modeling the bombers that came back without needing any more! This was termed "Survivor Bias." And furthermore, it was obvious that the areas that had the taken the least hits on the surviving bombers were the areas that must have been hit on the bombers that were lost.

So they armored the engines and cockpits, armoring especially the fuel lines at the engines and the aileron cables. The radial engine is a device of legendary robustness, continuing to operate even with whole cylinders blown away, but if it catches fire, it's often all over with. If your elevator cables are shot out you usually can use the elevator trim tabs to keep the airplane level and rudders are not essential unless you are doing acro. And both of those cables are accessible in the fuselage and can be repaired in flight with simple lightweight tools, but if aileron control is lost, it is time to bail out, and quick!

When the idea was first advanced people in the field scoffed. Armoring areas that we knew were not hit? Nuts! But after implementation began in mid-1943 the results were undeniable and astonishing. Losses dropped hugely.

Even the Germans noticed it. Adolph Galland said, "Something has happened to these bombers. A burst of fire that would have shot one down now barely even seems to slow them down."

Similar analysis was applied to the B-29, and in the early 1970's, no doubt taking into account the Vietnam experience the USAF added titanium-vandium armor on B-52's

I had never heard of this, despite being a life-long student of aviation, served 25 years on active duty in the USAF and after retirement worked 12 years for a company that did statistical analysis and modeling of failures for the Air Force, NASA, the FAA, and private firms.

That was great video on Youtube, although they insisted on showing a line drawing of a B-25 while talking about the B-17.

And speaking of the B-25, when I got here in 1993 I found that my next door neighbor had flown B-25's in the Med. He said that to his airplane he had added a sheet of steel on either side of the pilot's seat, enabling him to sit back and "drive" when they were flying through flak. I added that feature to a Revell 1/48 B-25 when I built a model for him. He said they almost never saw an enemy fighter but their unit had added tail gunner positions that looked rather like the ones on the B-25J and H.

You hear about crews adding extra armor to the aircraft but my friend Bob Berry said that sometime they took some of what was already installed back out. When Bob's PB4Y-2 was attacked by 12 George II fighters there was a head on pass that shot away one engine throttle, jammed the top forward turret and dumped the gunner on the floor, and wounded the other radio operator. Their seats were armored and an explosive round came in from the front and hit the armored seat back, between the radio operator and the seat back. The effect was like a shotgun blast, the shrapnel slicing into his back. They could not give him enough medical care at their base on Okinawa and he was evacuated back to Iwo Jima.

The crew decided that it was better to have the rounds leave through the side of the airplane rather than hit armor and rattle around the cockpit like a pinball machine, so they took out some of the armor that would facilitate that.

MIflyer said:

I had never heard of this, despite being a life-long student of aviation, served 25 years on active duty in the USAF and after retirement worked 12 years for a company that did statistical analysis and modeling of failures for the Air Force, NASA, the FAA, and private firms.

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I think it's just a fun story made up (or at least mostly made up) to explain survivorship bias.

Reading correspondence from the British officers/firms responsible for armouring aircraft -- they clearly understood (from the very beginning of the war) the implications of never finding returning aircraft with a particular area or component damaged.

It seems unlikely the US authorities were this unperceptive in this regard -- and I don't recall reading any British appraisals of US aircraft speaking negatively of their armouring (aside from the early, unprotected types, of course).

The story is an old meme dating back into antiquity. The principle is sound however and was often used by statistics professionals to explain why statistics have to be set in context otherwise having 40% of deaths on the roads being set down to drunken drivers would prove that drunken drivers are safer than the 60% who were sober.

Another one of these is steel helmets in WWI.

After the helmets were introduced it was noticed that the number of casualties with head wounds being treated rose massively. Of course people weren't getting head wounds because of the helmets, but people were surviving what would previously have been a fatal wound.