Editing Hotel-class submarine (section)

===Hotel II===
Beginning in 1961 and ending in 1963, all Hotels but one (''K-145'') were equipped with the new D-4 launch system, which could launch missiles from a depth of {{convert|16|m|abbr=on}}. The modified submarines received the [[NATO reporting name]] Hotel II. They were armed with [[R-21 (missile)|R-21 (SS-N-5 Serb)]] missiles, with a range of {{convert|1,200|km|nmi|abbr=on}}.<ref name="ref1996"/><ref>{{Citation
  | last = Jackson
  | first = Robert
  | title = Submarines of the World
  | publisher = Friedman/Fairfax Books
  | year = 2000
  | isbn = 1-58663-294-9 | oclc = 48261790
 }}</ref>  The installation of the D-4 launching system required some structural changes of the submarine; before launch, the launch tube had to be flooded. The chief designer of the modification was S.N. Kovalev.