You are comparing the hump on the 093B to the Arihant, which is based on the larger Akula class submarine, and which doesn't have a hump to begin with, so your graphic is misleading in the size comparison from the get-go. I doubt is even enough length in the flat part of the hump to provide space for 2 pairs of VLS silos, to speak nothing of 2 pairs of revolver-style VLS silos.Being used as a VLS is not implausible.
UUV docking station is more likely explanation than VLS IMO. Notice on the Amur how the flat part of the hump is quite significant and the slope is minimal, while on the 093B the flat part may even be less than the sloping part.Here is another example if you want to show a slight hump. This being an Amur, its a lot smaller.
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I was thinking that the hump might also be potentially for a small UUV.
This was probably the source of it all.
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Also we do know that the YJ-18 has sub launched versions. The question is which sub is launching it? Could it be a Type 093 or maybe the Type 032? Late end of the last year, engineering team for the sub launched YJ-18 got a commendation.
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There might actually be enough Type 093 satellite images, while blurry, to suggest that something is on its back.