Arjun Main Battle Tank (Mk-1 & Mk-2)

[Gautam]

A fantastic thread:

https://twitter.com/x/status/1936005769716957646

Patent on Arjun Mk.1A's CABIS (Containerized Ammunition Bin with Individual Shutters) with blowout panels.


Described as a 10-round bustle bin wherein each container has a separate shutter and whose plurality forms an annular space beneath the blowout panels which is interacted by the multiple apertures present on the containers as vents.




In case of initiation, the shutters act as mini blast doors and the gases are safely vented into the said annular space, the accumulation of which beyond a specified threshold value causes the blowout panels' fasteners to fail and give way to the rapidly expanding gases.
View attachment Arjun Mk1A_blowout_panel.mp4


The shutters are lever operated which work on a double plunger mechanism. The lever is coupled to a bracket (which is held in it's closed position by a compression spring) on which the two plungers are pivotally mounted.



The actuation of the lever from the upward to the downward position causes the bracket to rotate which leads to the compression spring to expand, as a result of which, the plungers are freed. The shutter may then be pulled open to access the content inside.



Which is suspiciously somewhat similar to the shutters used in the hull ammunition rack. The whole thing is pretty weird tbh, especially with its armour spec bulkhead plates and similar spec separation plates between the driver compartment & the nose fuel tank. Likely wet stores.




continued...

 

[Gautam]

continued from above...

The blowout panels are fastened to the roof along a frame (with sealant gaskets) via the means of screws or rivets as fasteners. These have a deliberate narrow neck portion which is supposed to break off during the venting process.



One plausible criticism of the CABIS is its complex nature utilizing the need of various individual shutters which serves no advantage over a conventional blast door (because all the rounds will get wasted regardless due to the supposed open apertures).

One might think, this potential issue could be / have been addressed in a similar analogy to the PA-171 transport pods which employ FRP PE ionomer vent windows (rated for sympathetic protection) which might face similar probable problems as the CABIS when bundled together.




But this is just my opinion so do not take it at face value. I just find it a bit absurd that the patent does not seem to even allude to this issue in the slightest.

A bit of a historical perspective. The Army had demanded ammunition containerisation & isolation with blowout way back in 1994 as one of the 10 JAP (Joint Action Plan) imperatives, which were imposed on the then early PPS (pre-production) Arjun tanks as bottom-line requirements.



Now this is my personal theory, but I think CVRDE couldn't fix the blowout until much later. This is evident from the remarks in the 2003 audit which state 9/10 JAP imperatives were met (including the ammunition stowage) and that containerization had been demonstrated.



As can be seen, no mentions of isolation or blowout.

This could only mean that a compromise was reached & the ammunition bin was rather worked in certain other aspects, like a quick drop-in magazine kind of system, with panels added as access ones which could be later repurposed as proper blowout ones as a form of future proofing.




This hypothesis is supported by the pictures of bustle panels on Arjun Mk.1s and Arjun Mk.2/1A prototypes, which are almost 1:1 identical. Difference being that Mk.1s do not have any individual shutters as Mk.1A's CABIS, therefore the panels are redundant in its case.