Norden Bombsight

[Greg Boeser]

One thing I wonder about is the role of Bombardiers and navigators and where they intersected. With the B-25 they had a bomb/nav, one man that did both jobs from his position in the nose. With the Martin B-26 in Europe they had both a bombardier and a navigator, with separate positions, although soon after takeoff it seems that the Nav went down to the nose and argued with the Bombardier over where they were, since both were trained both as navigators and bombardiers. Heavy bombers like the B-17 and B-24 seemed to have separate people in those positions, too.

By the way the Martin B-26 had the Norden bombsight, but in order for the bombardier to use the nose gun the bombsight had to be removed. I read of one mission where they were told to bomb an enemy troop concentration and then go down and strafe. The bombardier sighted through the Norden, dropped the bombs, and then as they turned around to strafe, removed the Norden and handed it to the Navigator, who held the bombsight while the Bombardier gleefully went to work with the .50 cal nose gun and the pilot strafed with the 4 package guns.

So how did they decide when they had a Bomb/Nav or separate positions?

Crew on the B-26 and the B-25 varied throughout the war based on the mission needs. As originally designed, both carried a crew of five, however the first B-26 units to deploy used crews of seven - pilot, co-pilot, navigator, enlisted bombardier, engineer, radioman and air gunner. B-25s carried a crew of six - pilot, co-pilot, navigator, bombardier, radioman, engineer/gunner. In the Pacific, a fully trained navigator was essential. The navigator's position was in a compartment directly behind the flight deck, so during flight it was common for the navigator to come forward and watch the action over the shoulders of the pilot and co-pilot. Once skip bombing was introduced, the bombardier was usually omitted from the crew to reduce manpower requirements, bombs being toggled by the co-pilot. However, even after most B-25s had been converted to strafer configuration, a few planes in each squadron retained the glazed nose for level bombing, each flight leader carrying a bombardier with bombsight, the others toggling on the lead ship's drop.
Mediums in North Africa and Europe generally carried a crew of six, combining the roles of bombardier and navigator in a single crewman, the "bombagator", though the lead planes usually carried a veteran lead bombardier and lead navigator. Low level ops proved too dangerous, so formation attacks at medium altitude became the standard procedure. Since precision group bombing placed more emphasis on concentration than individual accuracy, the "bombagator" or "togglier" toggled off their bombs when the lead ship dropped. The reason heavies retained fully trained bombardiers and navigators, while the function was combined in the mediums probably had to do with the greater demands placed on long range, high altitude operations compared to the shorter range missions at lower altitudes of the mediums. Regarding crew reductions, there were suggestions that mediums could dispense with co-pilots, since, it was said, their only real role was raising and lowering the landing gear. A block of B-26s, the B-26C-6, was produced without a co-pilot's position, but these were quickly retrofitted in the field by unit commanders.
Interestingly, the B-26 and B-25 were supplanted by the Douglas A-26, which had no co-pilot, the navigator assisting the pilot when necessary. Produced in glazed and solid nose configurations, it continued the practice of wingmen toggling on the lead ship's drop.

 

[stona]

At least the bombardiers can see the target at Cagliari. The average circular error in such good conditions was around 900 feet, which is not bad, if not exactly precise.

The real problem came when the target was obscured. In the 456 days from January 1944 to March 1945 visual bombing with the Norden sight, by the 8th AF, was only possible on 132 days. Other methods, like timed runs, were far less successful. In late '44 the 97th Bomb Group attacked Pilsen Skoda after a forty mile timed run, and missed by ten miles!

Senator Elbert Thomas (Utah), though he had religious and cultural reasons for his moral objections to strategic bombing, was not exaggerating by much when he said that precision bombing was "one of the outstanding hoaxes of military history".

Cheers

Steve

 

[billrunnels]

At least the bombardiers can see the target at Cagliari. The average circular error in such good conditions was around 900 feet, which is not bad, if not exactly precise.

The real problem came when the target was obscured. In the 456 days from January 1944 to March 1945 visual bombing with the Norden sight, by the 8th AF, was only possible on 132 days. Other methods, like timed runs, were far less successful. In late '44 the 97th Bomb Group attacked Pilsen Skoda after a forty mile timed run, and missed by ten miles!

Senator Elbert Thomas (Utah), though he had religious and cultural reasons for his moral objections to strategic bombing, was not exaggerating by much when he said that precision bombing was "one of the outstanding hoaxes of military history".

Cheers

Steve

Depends on how you define "precision". In my book 900 feet from 25,000 feet is precise.

 

[Tim Moore]

Daylight precision bombing has gotten a bad rap from a variety of angles. There are some points to be kept in mind:

1) It took several years to find out what targets were the most important strategically, especially oil refineries.

2) Results steadily improved during the war. General Lemay made two changes: He insisted on a straight run to the target without evasive action, and he chose the best bombardiers to be lead bombardiers, with the others in the group dropping on signal from the lead. The C-1 autopilot was introduced, allowing the bombardier to steer the plane much more accurately on the bomb run. The time over the target was increased. The types of bombs, particularly smaller ones, were changed, resulting in more accuracy. Finally, with air superiority won later in the war, it was possible to use lower bombing altitudes. What all this meant was that the Circular Error Probable (50% of bombs falling in a radius) went from 75 feet in prewar testing to around 1200 feet in 1943, but improved to 900 feet by 1945. When looking at how many bombs fell within 1000 feet of the target, this went from 10-15% in early 1943 to 40-60% in early 1945.

3) Defending against daylight precision bombing required an enormous amount of Germany/Luftwaffe resources, around the clock with the Americans by day and British by night.

 

[stona]

"Depends on how you define "precision". In my book 900 feet from 25,000 feet is precise."

I would agree, but it wasn't as precise as had been achieved back in the US, and it wasn't precise enough to make all the calculations done for the number of bombs (and bombers) required to destroy a target to be correct.
For example, Research showed that the 500lb M-43 with 267 pound of TNT created a crater two feet deep and nine feet in diametre in sandy loam with an instantaneous fuse.
If the calculations of the Bombs and Fuzes Subsection were correct (in fact they were too optimistic) the eight M-43s typically carried by a B-17 would damage 32,000 square feet. The Eighth Air Forces average circular error of 900 feet was an area 79 times greater!
Richard Hughes, then head of Eighth Air Force's Operational Planning Section concluded:

"The pre-war myth of a bomb in a pickle barrel from 20,000 feet was quickly exploded, and, to the intense disappointment of the regulars, it became apparent quickly that to destroy, or even to hit, a given target was going to call for a vastly heavier weight of attack than had been dreamed of in pre-war doctrine. Contrary to all expectations, with a few notable exceptions, the strategic bombers of the 8th and the 15th Air Forces seldom succeeded in achieving real precision bombing."

This is not a criticism of the men doing the bombing. I think you all did a remarkable job in unimaginably difficult circumstance. It is a result of huge over optimism among some senior, but still relatively young, airmen who developed the US pre-war doctrine. The doctrine quite literally developed around an unproven technology in the Norden sight. Good as it was, it was impossible to achieve anything like the experimental results operationally. It's why you and your comrades flew so often, for so long and in such huge formations. The eventual cost of the combined bomber offensive to the US and UK in treasure, but more importantly blood, was far in excess of anything anticipated.

A more fundamental problem for the US planners was the weather. It didn't matter how good a sight was, if the target was obscured by cloud it was useless. An air force and its personnel, assembled and supplied at a vast cost, cannot simply sit on its behind for three days out of four because of bad weather. The result, in a worse case scenario, was missing by ten miles.

Cheers

Steve

 

[Elmas]

"Error": difference between the value which has been computed and the correct value.

Let's assume a B17 that is going to do his final bombing run, as in the following picture. Please excuse the bad quality of the drawing, made in hurry.

Instruments say FL 25k, speed 220 kts.
FL: what is the error due to the instrument between the real value of FL and the indicated one?

Plus or minus 1%? 2%? 5%? 10%?

An error is certainly introduced into the sistem.

Speed. Again: 220 knt plus or minus 1%? 2%? 5%? 10%?

We are introducing another error.

And these are "readings from instruments". Now will see the "educated guesses".

Wind speed at FL and on the ground?

Direction of the wind at FL and on the ground? When Mistral is coming here in the Mediterranean you can have a gentle SE sea breeze on the ground but, looking at the clouds at 20k you can see them galloping in the sky from NW… Of course there could be some device to measure the drift, but again, what error in this device?

And now to things that are so aleatory that could not even be guessed.


How is the gradient of temperature and air density between GL and FL? The distribution will be linear as in B, increasing with the FL as in A or decreasing as in C?

For just this, different density of the air, a bomb can miss by hundreds of yards, not feet.

And all this for a bomber wich is flying all alone in a perfect route to a perfectly visible target.

But bombers fly in formation so, if the Leader is in the center and perfectly straight to the target the planes to the left and to the right will miss of more than 300 yards.

If we now add, like salt and pepper, Me-109s and Flak, and as tomato sauce the weather conditions of NE, we can easily understand that the words of Senator Elbert Thomas (Utah) were pure truth.

Of course: better to have a Norden than a lesser device or not to have a device at all: but Norden was certainly not a panacea.

 

[Hansie Bloeckmann]

A number of factors were considered when choosing the heading for the bomb run, flak concentration was one.

Thanks, Bill. As a large number of Allied bombers were "taken out" by German Flak batteries, I can clearly see why the AA batteries locations, as well as wind and climate conditions, could influence the flight path, both to target, and also for the return leg. Hansie

 

[Hansie Bloeckmann]

"Error": difference between the value which has been computed and the correct value.

Let's assume a B17 that is going to do his final bombing run, as in the following picture. Please excuse the bad quality of the drawing, made in hurry.

View attachment 482186

Instruments say FL 25k, speed 220 kts.
FL: what is the error due to the instrument between the real value of FL and the indicated one?

Plus or minus 1%? 2%? 5%? 10%?

An error is certainly introduced into the sistem.

Speed. Again: 220 knt plus or minus 1%? 2%? 5%? 10%?

We are introducing another error.

And these are "readings from instruments". Now will see the "educated guesses".

Wind speed at FL and on the ground?

Direction of the wind at FL and on the ground? When Mistral is coming here in the Mediterranean you can have a gentle SE sea breeze on the ground but, looking at the clouds at 20k you can see them galloping in the sky from NW… Of course there could be some device to measure the drift, but again, what error in this device?

And now to things that are so aleatory that could not even be guessed.


How is the gradient of temperature and air density between GL and FL? The distribution will be linear as in B, increasing with the FL as in A or decreasing as in C?

For just this, different density of the air, a bomb can miss by hundreds of yards, not feet.

And all this for a bomber wich is flying all alone in a perfect route to a perfectly visible target.

But bombers fly in formation so, if the Leader is in the center and perfectly straight to the target the planes to the left and to the right will miss of more than 300 yards.


View attachment 482187


If we now add, like salt and pepper, Me-109s and Flak, and as tomato sauce the weather conditions of NE, we can easily understand that the words of Senator Elbert Thomas (Utah) were pure truth.

Of course: better to have a Norden than a lesser device or not to have a device at all: but Norden was certainly not a panacea.

Elmas, could you please repeat that quotation here? I, for one, would very much like to hear it.

 

[Hansie Bloeckmann]

And another thing. That same Wikipedia article on Mary Brown talks about the bombsight being surrounded by "booby-trapped charges". Sheesh.

Mr. Moore raised a good point in his post. What "self-destruct" mechanisms were part of the Norden Bombsight- If B-17 was hit and crash landed (with the crew hopefully all parachuted out safely) and the aircraft and its components recovered by the Luftwaffe, would they be able to duplicate the Norden. Somewhere I read that the first series had a "cup" designed for the muzzle of a 1911-A-1 .45, or other issue USAAF sidearm, so that the bombardier or other crew member could shoot into that orfice and seriously damage the lenses--that might well be an "old wives' tale", like the one about an actress donating hair for the cross hairs of the aiming lens. Can anyone clarify this?? Thanks-- Hansie..

 

[Elmas]

Elmas, could you please repeat that quotation here? I, for one, would very much like to hear it.

Post #42 above, posted by Steve (stona)
"Senator Elbert Thomas (Utah), though he had religious and cultural reasons for his moral objections to strategic bombing, was not exaggerating by much when he said that precision bombing was "one of the outstanding hoaxes of military history".

 

[billrunnels]

Thanks, Bill. As a large number of Allied bombers were "taken out" by German Flak batteries, I can clearly see why the AA batteries locations, as well as wind and climate conditions, could influence the flight path, both to target, and also for the return leg. Hansie

They did a great job in planning the route.

 

[Tim Moore]

There was no self-destruct device in the Norden bombsight. The bombardier was to use his pistol and fire two shots into the rate end and one through the eyepiece. Pardini debunks this myth in his book, "The Legendary Norden Bombsight." There is mention in this book and in Hallion's book, "America's Pursuit of Precision Bombing, 1910-1945" of either a Mark 5 Mod 1 or Mark 15 Mod 1 destructive device designed by the Navy, but there are no records of it ever being installed or used. Likewise, there is mention of an 18" cylinder with 15 pounds of magnesium designed to be ignited and turned on the bombsight as a blowtorch, but this seem fantastical and no reports of this being used, either. (Imagine doing that while wearing an oxygen mask.) The confusion probably stems from the fact that there were thermite grenades on the bombers designed to destroy the entire aircraft, but nothing of this sort for the bombsight. Having restored dozens of Nordens, I have never seen any evidence of such a device.

 

[Tim Moore]

 

[stona]

The security measures were pointless as the Germans had details of the sight in 1938.

I've said before, nobody in their right mind would try to copy one of the Nordens of the type(s) in question. They might be more interested in how it solved the various elements of the 'bombing problem' but would be sensible to develop their own sight. I don't know if the Norden influenced German sights, there are as many opinions as people you ask!

It is a remarkable instrument, the Norden, but the principles on which it is based were hardly unknown to other nations.

Cheers

Steve