Sierra 3 or Mars was never built, scrapped on the slipways. It was going to have the first spherical sonar occupying the entire bow, the torpedoes being angled out behind it as in US navy practice. Frequently on sites like Fas, global security it is mistakenly claimed Sierra 2 had the bow sonar but the pics below clearly show that Sierra 2 had sonar below torpedo tubes suggesting cylindrical arrays.

But most obviously let’s suppose the hole is a shaped charge. Though perhaps a secondary explosion tears the bow apart would not some of the overpressure escape through the hole teaering it outwards? Also if a torpedo or other munition (the Granites are very close) cooked off in near proximity to this hole (torpedoes are nearby as is Granites) surely the secondary explosion would DESTROY the hole the mk 48 made. This suggests photoshop or salvage hole. Finally if the Russians were given hush money, one would expect them to keep their bargain wouldn’t one?

Pumpjets may have significant disadvantages. Weight is the obvious one but how about nonacoustic vulnerability? Could wake sensors detect pumpjets easier than normal propellers because the density of water change is greater (RSM55 suggested kolos may measure this) due to water being locally compressed in a short tube versus dispersed laterally (sideways) by a normal propeller? In other words just as putting your finger on a hose produces a short high mass spray (akin to a pumpjet) would not a lower density flow of water by a normal propeller produce less wake in that the wake is wider and more diffuse (and harder to distinguish from natural variation) rather than a small but highly concentrated change in water density from the narrow focussed efflux of a pumpjet? Remember the F117 echewed a conventional circular nozzle because the heat efflux is concentrated and disperses slowly whereas the thin wide efflux of the platypus exhaust dissipated Ir energy faster by increasing the surface area of efflux to the atmosphere cooling it faster. Thoughts anyone?