tag:blogger.com,1999:blog-5030145265861917845.post4707230588153156801..comments2024-03-28T14:35:30.147-04:00Comments on Tank Archives: ISU-122 Frontline ImpressionsPeterhttp://www.blogger.com/profile/09622237223229485503noreply@blogger.comBlogger5125tag:blogger.com,1999:blog-5030145265861917845.post-41325173427000065722021-02-24T16:05:45.764-05:002021-02-24T16:05:45.764-05:00Crabteeth: My reason for saying the part of the &q...Crabteeth: My reason for saying the part of the "broken nose" IS chassis, which was c. 65 mm thick and sloped at over 70 degrees, would resist even the Kwk43 at close range is found here:<br /><br />http://www.tankarchives.ca/2019/12/small-modernization-of-large-tank.html<br /><br />Specifically, this image:<br /><br />https://1.bp.blogspot.com/-LxMMr5etRv8/Xf6JvBDN6vI/AAAAAAAAhwI/BR8zpKzXQhce2FlsD-gxcMQl7fGe1kftgCLcBGAsYHQ/s640/is2dev3s05-e959e102baf81e49afec1594d782fa94.jpg<br /><br />Thus 'scuff marks' on the 70 degree sloped plate are from Kwk43 rounds. While they penetrated (as one would predict) the lower plate (100 mm at 31 degrees), and the plate containing the driver's plug vision port (120 mm at 30 degrees), they did not penetrate the 70 degree-plus sloped plate.<br /><br />I can't explain the penetrations in the photo you showed, except to say (admittedly questionable from the viewing angle) that the plate penetrated doesn't look like it's anywhere near 70 degrees of slope. Stewart Millenhttps://www.blogger.com/profile/01261690405884935161noreply@blogger.comtag:blogger.com,1999:blog-5030145265861917845.post-2425685385304670312021-02-24T04:41:44.143-05:002021-02-24T04:41:44.143-05:00Kellomies, we also know that not only hull front w...Kellomies, we also know that not only hull front was redesigned but also the front of turret did changed its appearence quite well. From different gun shield with shifted left side and gun sight together with it to mayor change of gun attachment in the tank. I think this match up with the time and effort to redesignation of SPGs if it was reccommended over ISU-122 S modification. Change of a gun mount would be the biggest challenge but you would get more internal space if you narrowed the front without cutting from the roof and sides in case even better slope would be needed.<br /><br />Stewart Millen, that upper hull plate is hardspot to AP rounds even in case of 'door kicker' but probably not in case of other types of shells. One vehicle got two direct hits there from something which resulted in two holes and lost to Finn hands.https://www.jaegerplatoon.net/ISU152_3.jpgCrabteeth RMhttps://www.blogger.com/profile/09715071498952492184noreply@blogger.comtag:blogger.com,1999:blog-5030145265861917845.post-63736869156958653042021-02-23T20:09:11.859-05:002021-02-23T20:09:11.859-05:00I'm more with Crabtree, Kellomies. Given that ...I'm more with Crabtree, Kellomies. Given that the ISUs began entry in 1944 (the first regiments weren't formed until May, it seems) it's already clear that even when they were being developed, their armor protection was problematic. I've done some crude measurements with online protractors and scale diagrams and conservatively estimated that it should have been possible to construct a single plate stretching from the lower plate to top of the casemate of 45 degress (that's a slope multiplier of 1.69, and about 150 mm of effective armor). <br /><br />Now, doing this would have lost the 70+ degree sloped 65 mm of armor part of the original IS-2 'broken nose' armor scheme, which was tough nut at close range even for the Kwk43. But as this great protection only forms a small percentage of the overall frontal surface, so improving the protection of the rest would still be a plus. However the gun mantlet (100 mm, somewhat rounded) would still be a weak spot (though the ISU-122S slightly improved that). A frontal plate of 150 mm of effective armor would have protected the ISUs well against Kwk36s and Kwk42s at normal engagement ranges for this beast.<br /><br />The problem I see is that the ISU-122 began as a spin-off of the ISU-152, a replacement for the SU-152. The 152 mm gun variants were originally designed as infantry support bunker blasters that *could* also fight tanks if need be. The ISU-122 shifts this emphasis to produce a long-range heavy tank destroyer that *could* also blow bunkers to bits if need be. Each could fill in for the other, but there was a shift in emphasis.<br /><br />The armor protection of the ISU-152 was fine for a fight at medium range (c. 1000 meters) against infantry supported only by Pak40s or assault guns bearing the Pak40. It's not fine if your opponent is enemy tanks bearing better guns than the Pak40. When the ISU-122 was in the design phase, the Panther and Tiger I had been out for months and the Ferdinand and Kwk43s had come out at Kursk too. I find it strange, as I have said, that the T-34 team kept rejecting what I think were good proposals for improving the T-34's armor which would have made it almost impervious to the Pak40 at everything except maybe the closest ranges, and much more resistant to Kwk36s and Kwk42s, only because it wasn't good enough to stop the Kwk43, while the team working on the ISUs (and the ISU-122 was designed to take on those very same German heavies) were fine with armor that was 'meh' at best against those guns. That does not compute.Stewart Millenhttps://www.blogger.com/profile/01261690405884935161noreply@blogger.comtag:blogger.com,1999:blog-5030145265861917845.post-44743366583418244262021-02-23T13:03:37.677-05:002021-02-23T13:03:37.677-05:00You mean they sloped the IS-2 hull front to get ri...You mean they sloped the IS-2 hull front to get rid of that KV-legacy "step". Straightforward enough and made for few enough differences to the internals.<br /><br />Doing the same to the ISU casemate would have been a MUCH bigger deal requiring at the very least a nontrivial redesign of the gun mounting, and sloping the front enough for actually meaningful protection gains oughta have demanded revising much of the fighting compartement.<br /><br />Considering these were meant to be (relatively) "cheap and cheerful" standoff fire-support designs that brought more big guns to the frontlines on budget that doesn't sound like a very sensible project to embark on to me, especially with the end of the war and the replacement of the base tank already in sight.<br /><br />Compare the Object 704 which was designed from the ground up with proper sloping in mind and apparently still ran into working-space issues...Kellomieshttps://www.blogger.com/profile/04915110653443066212noreply@blogger.comtag:blogger.com,1999:blog-5030145265861917845.post-91454578101552135022021-02-22T15:39:44.422-05:002021-02-22T15:39:44.422-05:00Finally some report which evaluate the armor prote...Finally some report which evaluate the armor protection. The fact that it not always protected from AT gun is just how many expected. There should be specified which gun with caliber of 88 mm can penetrate its armour at 1800 m. The german SPGs with armor protection level against the AT guns have the same or better armor protection than tank on which basis they are built on. For Soviet SPGs its in opposite direction except the SU-100/85 M. If they narrowed the nose of IS-2 to simplify the production and increase the protection, I think the similar thing should be done in case its SPGs.Crabteeth RMhttps://www.blogger.com/profile/09715071498952492184noreply@blogger.com