Drawing of the 4 different, currently thought to be active, versions of russian Akula class submarines. Starting with boats of the first flight/batch on the bottom, followed by the 2nd flight and finally showing the two variants of "Akula 2" class submarines in the upper half.
<a href="//commons.wikimedia.org/wiki/User:Alexpl" title="User:Alexpl">Alexpl</a>
CC BY-SA 3.0
<span class="int-own-work" lang="en">Own work</span>, based on the information detailed above