The Republic of Korea Navy has about 160 ships in commission (a total displacement of about 232,285 tonnes). The vessels are categorized into four levels. A first-rate ship (Sohn Wonyil-class SS, DDG, DDH, LPH, MLS, and AOE) is commanded by a captain; a second-rate ship (SS, FFG, FF, PCC, LST, ATS, and ASR) by a commander; a third-rate ship (PKG, MSH, and MHC) by a lieutenant commander; and a fourth-rate craft (PKMR, PKM, and LSF) is commanded by a lieutenant or a warrant officer.