Barnes Wallis, Earthquake bombs and TARZON with radar.

[Draconis]

Inspired by recent comments in the Keynes' cruisers story I offer this speculation about how to build a precision guided Tallboy-like all weather bomb using late WW2 technology.

https://en.wikipedia.org/wiki/ASM-A-1_Tarzon

This wikipedia article describes one version of the radio controlled bombs deployed by the Allies late in the war. A key point is they were steered unto their target by the operator visually tracking the bomb which had a flare attached to its tail so as to improve its visibility to the operator. This required daylight operations only in clear or nearly clear weather conditions.

Could these and similar heavy weight bombs have been dropped using radar guidance? Did the USAAF H2X radar of 1945 have the resolution to identify large structures like power stations, industrial complexes or dams. Or ships at sea?

If so then instead of the bomb being fitted with flares for visual tracking have instead a very low power radio transmitter on the same frequency as the H2X radar be fitted to the bomb. Very low power so as to not jam the radar return but instead it would show as a small dot on the radar scope. Also a low power SHF (less than 1 watt) transmitter would not require the cavity magnetron and a large power supply.

The radar operator would find and identify the target. The bomb would be dropped and the bombardier using the same or possibly a repeater scope would steer the dot onto the radar target using the same RAZON system. This system allows high altitude precision bombing at night and/or in overcast conditions. Opening up many important targets to precision bombing with Tallboys and Grand slam earthquake bombs while reducing the risk to the flight crews since they would bomb at night from at least 30,000 feet.

Ships at sea would also produce a strong radar return. This system could be used for attacking even the largest enemy warship. Even the Yamato would not have survived Tallboy or Grand slam hits. It wouldn't take many. And if it had been attacked at night from 30,000 feet they might not have even know they were being attacked meaning no evasive maneuvering. However if this system works even a maneuvering ship would still be hit.

If something like this had been worked up in 1942 than Barnes Wallis' designs would have shortened the war.

 

[Sbiper]

snip

Short answer - no

Could these and similar heavy weight bombs have been dropped using radar guidance? Did the USAAF H2X radar of 1945 have the resolution to identify large structures like power stations, industrial complexes or dams. Or ships at sea?.

Ships only, maybe bridges if you used the larger six foot scanner and went to 3cm as opposed to 10cm.

If so then instead of the bomb being fitted with flares for visual tracking have instead a very low power radio transmitter on the same frequency as the H2X radar be fitted to the bomb. Very low power so as to not jam the radar return but instead it would show as a small dot on the radar scope. Also a low power SHF (less than 1 watt) transmitter would not require the cavity magnetron and a large power supply

The radar operator would find and identify the target. The bomb would be dropped and the bombardier using the same or possibly a repeater scope would steer the dot onto the radar target using the same RAZON system. This system allows high altitude precision bombing at night and/or in overcast conditions. Opening up many important targets to precision bombing with Tallboys and Grand slam earthquake bombs while reducing the risk to the flight crews since they would bomb at night from at least 30,000 feet.

It could have been done, but look at the history of early (pre late 1960's PGM's) and you can see that they were less than effective overall. It was only with the advent of IC's and Lasers that PGM's really became practical. The system you describe is essentially a SARH (Semi Active Radar Homing) system with command guidance - the preferred guidance method for early SAM's afaik the Soviets only stopped using it from the SA-6 onwards.

If something like this had been worked up in 1942 than Barnes Wallis' designs would have shortened the war.

Unlikely IMHO. You have to remember that 'modern' PGM's came about because of a very specific requirement by the USAF - to drop railway bridges in North Vietnam. Laser guided weapons came from that one requirement, oh there had been PGM's prior to that but they had essentially been useless. All modern PGM's can pretty much trace their lineage back to this single task - absent this task and PGM's might have taken another decade or two to evolve. Where is the Operational Requirement for a PGM by the RAF in WW2, especially in the early years? This is a service that still thought its crews could precision bomb at night over the Ruhr with nothing more sophisticated than a stopwatch, a sextant and a course setting bombsight.

 

[AlanJWhite]

One problem is that Tarzon is based on a Tallboy but with over half a ton of added guidance = 5.9 tonne.

A standard B-29 cannot carry that load to 30,000 ft for any practical distance
and no other aircraft can get close to that height (certainly before WW2 ends)
Aside; It was too big to fit even into a B-29 and had to be carried externally in Korea
Lancs carrying the standard Tallboy had to be modified, The halifax ... hah

Add in the fact that even 1945 Radar cant distinguish the kind of target you suggest
(see Sbipers analysis above and elsewhere)

Plus the vulnerability of any 1940 radio control to Jamming (see Fritz X and Hs-293)

and BTW: 30,000 ft is NOT safe from late WW2 Flak .. especially with VT Fusing

In 1942, the correct weapon for the RAF is a earthquake bomb that can be carried by many aircraft types with minimal mods.
essentially in the 4000lb range.... what I jokingly christened the "Small Boy".
Aside: this smaller size could be carried even by a B-17

It would have less absolute penetration but would still create a vast crater or earthquake or camouflet i.e. create an subterranean void depending on height dropped.
By itself it could tackle many rail and road hubs but would also be suitable for factories etc when used in concert with better blast bombs like the Cookies or Incendiaries like th Clusters in OTL.

Initially it would be a sniper weapon as OTL but soon used by part of the main force.
Therefore Small Boys would need to be available in far larger numbers than the OTL designs ..
but could be adapted for mass production as the USA was later able to do for Tall Boy.

Of course The RAF would need better operational practice and better targeting to get the best results in 42 at night.
By day in 1943 the USAAF would need to drop the idea of "Group Bombing" if they adopted this weapon
(however with the Norden already in every aircraft they had a suitable sight to use its benefits)

And since a B-29 could carry a Smallboy internally, then perhaps accurate bombing of Japan in 44 might be possible (despite the problems with the Jet stream)
Which might just avoid the switch to area firebombing of civilian areas that killed more civilians than the A Bombs.

 

[Gunnarnz]

Which might just avoid the switch to area firebombing of civilian areas that killed more civilians than the A Bombs.

Perhaps, but I wouldn't count on it. There was nothing accidental about the firebombing of Japanese cities (or German ones, for that matter). It was a deliberate attempt to attack enemy industrial capacity by at best dehousing workers, and in the end attempting to kill, wound, or scare off as many of them as possible. From that point of view civilian casualties are a feature, not a bug, of the chosen attack method. I'm not at all sure that the availability of more precise bombs would lead to a change in the policy.

 

[marathag]

Ships only, maybe bridges if you used the larger six foot scanner and went to 3cm as opposed to 10cm.

The BAT glide bomb was tweaked to be able to hit bridges. BAT was S-Band

And news to me, dropped from F4U.
Interesting.

 

[marathag]

You have to remember that 'modern' PGM's came about because of a very specific requirement by the USAF - to drop railway bridges in North Vietnam.

Bullpup predated that need(1959), and were just too small a warhead to drop spans

 

[marathag]

A standard B-29 cannot carry that load to 30,000 ft for any practical distance
and no other aircraft can get close to that height (certainly before WW2 ends)
Aside; It was too big to fit even into a B-29 and had to be carried externally in Korea

Number I have for range are
1550 miles for 20,000 pounds
1900 miles for 10,000 pounds
2666 miles for 2000 pounds

External racks for a pair

But the tradeoff for bombload is fuel.

B-29 has 60,000 pounds of payload.

It can be over 20,000 pounds of bombs, at the cost of range.

B-29 was tested with the T-14 aka Grandslam and the larger 42,000 pound T-12 'Cloudmaker'

Each gallon of AvGas is around 6.5 pounds, 400 gallons per hour of operation. How far do you want to go?

 

[AlanJWhite]

Number I have for range are
1550 miles for 20,000 pounds
1900 miles for 10,000 pounds
2666 miles for 2000 pounds


How far do you want to go?

Basically I think for WW2
in the ETO East Anglia to Berlin is a good yardstick (500 miles radius)
in the PTO Okinawa to Tokyo similarly (1000 miles radius)

Later for Korea
S japan to Seoul (~ 350 miles radius)
Kadena (where most of the B-29s used for the few TAZON combat missions were based) is more

AIUI (and admittedly my sources are poor/secondary for American Aircraft) more realistically the B-29 did

• 5,000 lb over 1,600 mi radius at high altitude
• 12,000 lb over 1,600 mi radius at medium altitude
• 20,000 lb maximum over short ... effectively tactical ... distances at low altitude

Even one Tazon is 13,000 lbs and acts worse because it creates more drag than an internal load.

On that basis I think that my original conclusion stands
if you are trying for a true "earthquake" effect with significant ground penetration.
However if what is required is a medium sized "blast" bomb with a great accuracy then ...

Aside: I say only medium sized because Tallboy only carried 5,200 lbs of Torpex (in 12,000 total)
while the Cookie Series of blast bombs went up to 9,000 lbs Torpex (in the same total weight)

 

[AlanJWhite]

Perhaps, but I wouldn't count on it. There was nothing accidental about the firebombing of Japanese cities (or German ones, for that matter). It was a deliberate attempt to attack enemy industrial capacity by at best dehousing workers, and in the end attempting to kill, wound, or scare off as many of them as possible. From that point of view civilian casualties are a feature, not a bug, of the chosen attack method. I'm not at all sure that the availability of more precise bombs would lead to a change in the policy.

For both the RAF and the USAAF the use of "Area" bombing and large amounts of incendiaries by night WAS a deliberate choice but that does not mean it was a preferred choice and certainly not the first method they attempted.

In each case the switch was forced on them by the practical failure of their planned methods
i.e. cost effective bombing of industrial targets from high level in daylight.
For the RAF in 1940 the deciding factors were too high a casualty rate and too poor accuracy
and for the USAAF over Japan in 1944 the decision was forced by being unable to hit such targets at all
(mostly due to terrible accuracy because of unexpected local air conditions not defensive strength).

My point was that simply having a consistently falling earthquake bomb that their available aircraft could carry
might have made the USAAF's attempt at accurate bombing over Japan practical thereby
forestalling LeMay's desperate need to justify the vast expense of his squadrons
even if meant abandoning his sacred Douhet and Mitchell principles.
In effect he adopted the very same tactics that the USAAF had derided when used by the RAF in the ETO
and they worked

(as did the USAAF Starvation campaign of naval mining equivalent to the RAF Gardening missions
... but that is a different argument)

 

[Draconis]

Here is an old article that marathag posted in another thread. The radar pictures are informative in depicting the improved resolution of the APQ-7 equipment that was becoming available in 1945.

The improved resolution of the radar imagery of the APQ-7 is clearly evident. By comparing the topographic radar picture to photographs of the area the targets' location can be pinpointed even if there is no identifiable radar return from the target itself. That location would then have the radar dot of the RT-RAZON steered onto it. Most likely having several bombs serially dropped within a 5 to 10 minute period. Day or night and irregardless of cloud cover.

Of course the accuracy and reliability of this first generation PGB would've been poor compared to modern day Paveway and GPS targeting systems but I think it would have been a big improvement over the visually steered RAZON and AZON of OTL and a huge improvement over the OTL conventional bombing. As mentioned in my OP put this system on the biggest bombs that Allied aircraft can carry for the precision attack on key and vital enemy infrastructure and industries.