Further Analysis Of North Korea's New Missile Submarines
A major question is whether ‘Hero Kim Gun-ok’ is the same submarine which was showing in 2019 when Kim Jong Un visited Sinpo. That boat, known in the West as Sinpo-C, was undergoing conversion to carry missiles. The temptation is to say that it is probably the same submarine. However, a comparison if the available imagery identifies significant and numerous differences.
If they are the same submarine, then the subsequent modifications after 2019 are extreme. It would be as if they rebuilt it twice, and also changed minor details along the way. A more straightforward explanation is that there are at least two ROMEO class submarines undergoing modification.
Sinpo-C had telltale signs that it was being modified to carry much larger ballistic missiles, like the Pukguksong family. There were vent holes in the upper sail consistent with the Gorae class test submarine, which launches these missiles. Pukguksong are strategic missiles, yet Hero Kim Gun-ok is described in North Korean sources as having a tactical relevance.
One explanation is that the two sets of conversion are aimed at building both 'strategic' and 'tactical' missile submarines. Both could however carry nuclear weapons, so the term 'tactical' is contextual.
The strategic submarine, Sinpo-C, can likely carry three large Pukguksong missiles. It is in some respects a more limiting conversion of the ROMEO class however. It appears that, unlike on Hero Kim Gun-ok the missiles impinge on the aft battery compartment. Hero Kim Gun-ok on the other hand has had a ~15 meter hull insertion between that compartment and the command center. We can infer that Hero Kim Gun-ok likely has a greater underwater endurance on batteries, similar to the unmodified ROMEO.
Hero Kim Gun-ok may have made compromises in the torpedo room area however, while Sinpo-C still had the entire forward bow intact.
Small details also suggest that they are conversions of different ROMEO class boats. Hero Kim Gun-ok features the unusual 'Chinese style' angle snort mast fairing. This appears shorter since the sail beneath it has been raised around its base. It therefore likely no longer has the benefits it was designed for. The most straightforward explanation is that the submarine it was built from already had it. Although it is difficult to be sure in the available imagery, Sinpo-C does not appear to have this.
CLICK to Enlarge. The lines of the missile tube fairing (A) are completely different, despite Sinpo-C already having vent holes (B) indicating missile tubes in its sail. The snorkel mast fairing (C) appears different, and the hand rails (D) extend further along the sail on Sinpo-C. Sinpo-C appears to have several windows in the bridge (E) while Hero Kim Gun-ok's are only two and appear slightly higher up. Possibly these are now only navigation lights since the hydroplanes (F) mechanism now occupies this space. There is no dsign of this on Sinpo-C.