Pz.Kpfw. III with short 7,5 cm guns

Discussions on the vehicles used by the Axis forces. Hosted by Christian Ankerstjerne
Lars Bertelsen
Member
Posts: 402
Joined: 16 Apr 2006, 10:02
Location: Denmark

Pz.Kpfw. III with short 7,5 cm guns

#1

Post by Lars Bertelsen » 06 Aug 2015, 21:53

Hello

I use to stay in the Fortifications&Artillery section, but this topic is rather an AFV one.
The attached copy (from W.A.Boelcke: Deutschlands Rüstung im Zweiten Weltkrieg) should be a note from Albert Speer made after his conference with Hitler 19.-22. August 1943.
The 3 guns mentioned in the note must be:
5 cm KwK L/42 rebored = 7,5 cm KwK 68 L/20
5 cm KwK 39 L/60 rebored = 7,5 cm KwK 67 L/24
5 cm Pak 38 rebored = 7,5 cm PAK 50 L/30 .

The 7,5 cm KwK 68 was probably never produced, but a number of the 7,5 cm KwK 67 and the 7,5 cm Pak 50 were finished.

On the conference 30. September to 01. October 1943 (see attachment), it was considered to use the rebored KwKs in fixed mountings. This might indicate that these guns were originally designed for another purpose.

The KwK 67 and the KwK 68 could seem to be an easy way to convert the 5 cm gun of any Pz.Kpfw.III into a short 7,5 cm weapon (or to rebuild the vehicle into a Pz.Kpfw.III Ausf. N, so to speak). But was this ever done in any case?

According to Chamberlain & Doyle, a total of 663 Pz.Kpfw.III Ausf. N were finished by August 1943, and a further 37 were converted from rebuild Pz.Kpfw.III. The 37 rebuild vehicles might be Pz.Kpfw.III with rebored guns?

greetings
lars
Attachments
430822_Boelcke.jpg
431001_Boelcke.jpg

User avatar
Christian Ankerstjerne
Forum Staff
Posts: 14027
Joined: 10 Mar 2002, 15:07
Location: Denmark
Contact:

Re: Pz.Kpfw. III with short 7,5 cm guns

#2

Post by Christian Ankerstjerne » 07 Aug 2015, 12:38

Do you know the months during which these guns should have been finished? I might be able to find some information in the production records.


User avatar
mark67
Member
Posts: 141
Joined: 21 Aug 2003, 14:38
Location: Warsaw, Poland

Re: Pz.Kpfw. III with short 7,5 cm guns

#3

Post by mark67 » 07 Aug 2015, 18:29

According Panzer Tracts under Umbewaffnung Programm there were rebuild 69 tanks Panzer III to Ausf N standard . There are two survivors of such converted tanks - recovered in Norway in 2006. Those existing examples have replaced whole turret by standard one for Ausf N with normal KwK 37 L/24.

User avatar
peeved
Member
Posts: 9109
Joined: 01 Jul 2007, 08:15
Location: Finland

Re: Pz.Kpfw. III with short 7,5 cm guns

#4

Post by peeved » 07 Aug 2015, 19:55

According to Boelcke on 4 June 1942 Speer wrote
Die kurze 7,5 cm KwK L 24 soll gemäß unserem Vorschlag nicht neu anlaufen, sondern die vorhandenen 450 sollen in den Monaten Juli, Aug., September im jetzigen Turm des Panzer III als einmalige Serie eingebaut werden.
Gegebenfalls sind die 150 weiteren Rohre noch mit Bodenstücken und Verschlüssen zu versehen und anschließend ebenfalls einzubauen.
Thus the plan appears to have been to use 450 existing 7,5 cm KwK 37s and using available barrels to assemble 150 more for the Pz. III Ausf. N for a total of 600 which is a bit less than the actual production. However since 524 more KwK 37s were manufactured 1939-42 than short-barreled Pz.IVs according to "Waffen und Geheimwaffen des Deutschen Heeres 1933-1945, Band 2" by Fritz Hahn and rearming the latter with KwK 40 freed KwK 37s for Pz. III use there probably were enough for the whole Ausf. N production run (even though the KwK 37 was used in other projects to a lesser degree).

Markus

Edit: Also if the conference concerning rebored 5 cm KwK was held in August 1943; The month when Ausf. N production ended, the timeline suggests that KwK 67s were not used to arm it.

Lars Bertelsen
Member
Posts: 402
Joined: 16 Apr 2006, 10:02
Location: Denmark

Re: Pz.Kpfw. III with short 7,5 cm guns

#5

Post by Lars Bertelsen » 09 Aug 2015, 23:52

Hello

In October 1944 it was decided to convert 700 5 cm KwK 39 L/60 into 7,5 cm KwK 67 L/24, and in November 550 guns were rebored. But these guns came all from stockpiles and were earmarked for fixed mounts, not vehicles. Some KwK 67 guns from emplacements near the Oder were recovered after the war. This shows that the rebored guns were actually used in combat.
But this says nothing about rebored guns in vehicles.

It is correct that the conference in August 1943 were about same time as the PzIII production stopped. But the last 8 converted PzIIIs were not finished until 1944 (Chamberlain&Doyle, page 263).
But we miss further informations (and photos) to conclude anything about this.

Interesting that the two recovered PzIIIs in Norway were fitted with new L/24-turrets. But again, it might seem to have been much easier to rebore the guns in the existing turrets. The original turrets may have been damaged, or there might be some other reason?

Production numbers according to Fritz Hahn and Chamberlain&Doyle:
7,5 cm KwK 37 L/24: 1446
Pz.Kpfw. IV with 7,5 cm KwK L/24: 1125
Pz.Kpfw. III with 7,5 cm KwK L/24: 700
It must be correct that the missing guns were taken by upgrading PzIVs with new L/43 or L/48 guns.

We still do not know why the rebored KwK 67 and KwK 68 were developed. They were later intended for use as coastal defense guns, but this was not the original intended purpose.
The two gun types were originally designed to fire a relatively light 5 cm round, so maybe the original PzIII turret for a 5 cm gun was simply not able to resist the recoil force of a rebored gun firing a much larger round?
The recoil force of the KwK 67/68 was 8200 kg, according to German manual from 1944. Does anybody know the recoil force of the 7,5 cm KwK 37?

lars

Alanmccoubrey
Member
Posts: 3369
Joined: 19 Sep 2008, 14:44

Re: Pz.Kpfw. III with short 7,5 cm guns

#6

Post by Alanmccoubrey » 12 Aug 2015, 21:47

Lars, How would you account for the 7,5cm L/24 guns used in the various types of STUMMEL, the SdKfz 250/8, SdKfz 251/9, SdKfz 233 and SdKfz 234/3 ?
Alan

Lars Bertelsen
Member
Posts: 402
Joined: 16 Apr 2006, 10:02
Location: Denmark

Re: Pz.Kpfw. III with short 7,5 cm guns

#7

Post by Lars Bertelsen » 12 Aug 2015, 23:13

Hello

Apart from the KwK 67, four types of 7,5 cm L/24 guns are known (KwK 37 – StuK 37 – K 37 – K 51).
Sd.Kfz. 251/9 (“Stummel”): K 37 (early) / K 51 (late).
Sd.Kfz. 250/8: K 51
Sd.Kfz. 233: StuK 37
Sd.Kfz. 234/3: K 51

AFAIK the four types were almost identical. The K 51 is easy to distinguish from the others because the breech block was cut in a sharp angle and not rounded like on the other three types, but this seems to be the only major difference.
The K 37 in the Sd.Kfz. 251/9 (and probably the StuK 37 in Sd.Kfz. 233 too) used the same carriage as the StuK 37 in the StuG III, only the gun mantlets were different. And the KwK 37 used yet another different gun mantlet designed for a rotating turret, but the gun itself was most probably the same.

According to Fritz Hahn and other sources, it might seem that the production numbers of 7,5 cm StuK 37 + K 37 exaggerated the number of vehicles using these guns. But I am not sure that I have got the right information.

greetings
lars

User avatar
peeved
Member
Posts: 9109
Joined: 01 Jul 2007, 08:15
Location: Finland

Re: Pz.Kpfw. III with short 7,5 cm guns

#8

Post by peeved » 12 Aug 2015, 23:27

Lars Bertelsen wrote:Production numbers according to Fritz Hahn and Chamberlain&Doyle:
7,5 cm KwK 37 L/24: 1446
Pz.Kpfw. IV with 7,5 cm KwK L/24: 1125
Pz.Kpfw. III with 7,5 cm KwK L/24: 700
It must be correct that the missing guns were taken by upgrading PzIVs with new L/43 or L/48 guns.
Reading Hahn closer it appears to me that his production figures are for wartime only so the 1446 appears too low for total KwK 37 production during all of 1939-42. As for the 1125 number it likely includes somewhat over 200 pre-war Pz. IV shorts.
Lars Bertelsen wrote:We still do not know why the rebored KwK 67 and KwK 68 were developed. They were later intended for use as coastal defense guns, but this was not the original intended purpose.
How do we know that? In fact could not coastal defence have been the original intention since to my knowledge it appears to have been the use first put forward to and agreed by Hitler in September/November 1943. No intended purpose seems to have been discussed in the August conference where AH expressed his delight over the possibility to rebore 5 cm guns.
Lars Bertelsen wrote:The two gun types were originally designed to fire a relatively light 5 cm round, so maybe the original PzIII turret for a 5 cm gun was simply not able to resist the recoil force of a rebored gun firing a much larger round?
The recoil force of the KwK 67/68 was 8200 kg, according to German manual from 1944. Does anybody know the recoil force of the 7,5 cm KwK 37?
The recoil force doesn't appear excessive to me for a Panzer III; however the existing 5 cm KwK recoil systems may have been too weak. It is possible to calculate ballpark figures for average KwK 39 and KwK 37 recoil force through dividing the recoil energy figures derived from below in "Waffentechnisches Taschenbuch" by g*lr where lr is the normal length of recoil.
KwK 39: mp=2,06 kg, mc=0,91 kg, v0=835 m/s, mr=255 kg and lr=0,32 m yield ca. 5270 kg recoil force which suggests that the 8200 kg was a bit too much for the mounting. I'd imagine that the shortened and rebored KwK 67 had quite a bit less recoiling parts' weight than the original KwK 39 which together with short recoil length made the 67 a heavier kicker than the
KwK 37 for which mp=6,8 kg, mc=0,41 kg, v0=385 m/s, mr=285 kg and lr=0,43 m yield ca. 3890 kg recoil force.
A reference to recoil problems with KwK 67 down low from the text of "Bericht Nr.2" "Stand der Entwicklung am 18.2.1945" (Rheinmetall-Borsig) dated 5.3.1945 and quoted in Waffen-Revue Nr. 113.

Markus
Attachments
PICT0049.JPG
PICT0047.JPG

Lars Bertelsen
Member
Posts: 402
Joined: 16 Apr 2006, 10:02
Location: Denmark

Re: Pz.Kpfw. III with short 7,5 cm guns

#9

Post by Lars Bertelsen » 13 Aug 2015, 23:22

Hello

You may be right about the two quotes from Boelcke in my first post. The rebored guns are first mentioned by Speer in August 1943, and in September/October he writes that the guns can be used with the Einheitssockellafette. When reading Boelcke’s text, my first impression was that the decision about the Einheitssockellafette was not made until the September/October meeting, but maybe it was made already in August.

Thanks for your attachments. The KwK 67 was surely not developed for the Sockellafette Ib, which was not designed until late 1944. Originally for the 5 cm KwK 39, the information about the KwK 67 is new to me. 200 Sockellafetten Ib were planned in January 1945, but most likely no one was ever finished.
The last information in your copy, however, must be an error. It is certainly not possible to mount a Pak 43 barrel in a Sockellafette Ic.

greetings lars

User avatar
peeved
Member
Posts: 9109
Joined: 01 Jul 2007, 08:15
Location: Finland

Re: Pz.Kpfw. III with short 7,5 cm guns

#10

Post by peeved » 14 Aug 2015, 23:24

Lars Bertelsen wrote:The KwK 67 was surely not developed for the Sockellafette Ib, which was not designed until late 1944.
Quite so. I was merely trying to illustrate how excessive recoil seems to have plagued the KwK 67 project.
Lars Bertelsen wrote:The last information in your copy, however, must be an error. It is certainly not possible to mount a Pak 43 barrel in a Sockellafette Ic.
Weightwise it does seem a hefty load; 2200 kg total gun weight for Jagdpanthers' Pak 43/3 and Pak 43/4 according to Spielberger's Panther book although the average trunnion pull was just 6300 kg even on that mounting with a normal recoil length of only 0,55 m compared to the low elevation recoil of 1,25 m on the field carriage.

BTW according to Spielberger's Pz. IV book the average trunnion pull of 7,5 cm KwK L/24 was 4500 kg at zero elevation and 430 mm recoil; ca. 15% more than my previous ballpark calculation but still significantly less than KwK 67/68's.

Too bad there seems to be no record of the bored-out KwKs being present at the "Vorführung neuer Waffen" on 1 October 1943, there is at least photographic evidence of a 7,5 cm Pak 50 being exhibited.

Markus

User avatar
peeved
Member
Posts: 9109
Joined: 01 Jul 2007, 08:15
Location: Finland

Re: Pz.Kpfw. III with short 7,5 cm guns

#11

Post by peeved » 15 Aug 2015, 21:41

peeved wrote:Too bad there seems to be no record of the bored-out KwKs being present at the "Vorführung neuer Waffen" on 1 October 1943, there is at least photographic evidence of a 7,5 cm Pak 50 being exhibited.
Hmm... What would a factory rebuilt Ausf. N do at an October '43 "new weapons display"... or is this a KwK 67 technology demonstrator?

MarkusImage

Alanmccoubrey
Member
Posts: 3369
Joined: 19 Sep 2008, 14:44

Re: Pz.Kpfw. III with short 7,5 cm guns

#12

Post by Alanmccoubrey » 16 Aug 2015, 19:59

Markus, I'd say you were correct there, unless of course they are demonstrating the full recoil on a very old L42 armed tank.
Alan

Lars Bertelsen
Member
Posts: 402
Joined: 16 Apr 2006, 10:02
Location: Denmark

Re: Pz.Kpfw. III with short 7,5 cm guns

#13

Post by Lars Bertelsen » 16 Aug 2015, 22:56

Thanks for the picture Markus. It does not look like a 7,5 KwK 37, so it must indeed be a 7,5 cm KwK 67.
greetings lars

User avatar
peeved
Member
Posts: 9109
Joined: 01 Jul 2007, 08:15
Location: Finland

Re: Pz.Kpfw. III with short 7,5 cm guns

#14

Post by peeved » 17 Aug 2015, 14:48

Here is a bit better version of the Pz. III with probable KwK 67.

Markus
Attachments
KwK67c.png

User avatar
peeved
Member
Posts: 9109
Joined: 01 Jul 2007, 08:15
Location: Finland

Re: Pz.Kpfw. III with short 7,5 cm guns

#15

Post by peeved » 17 Aug 2015, 14:50

...and here the rest of its shots I found on BPK.

Markus
Attachments
KwK67.jpg
KwK67b.jpg
KwK67a.jpg

Post Reply

Return to “The Ron Klages Panzer & other vehicles Section”