| Country | Military branches |
| Slovakia | Armed Forces of the Slovak Republic (Ozbrojene Sily Slovenskej Republiky): Land Forces (Pozemne Sily), Air Forces (Vzdusne Sily) (2010) |
| Slovenia | Slovenian Army (includes Air and Naval Forces) |
| Solomon Islands | no regular military forces; Solomon Islands Police Force (2011) |
| Somalia | National Security Force (NSF): Somali Army (2011) |
| South Africa | South African National Defense Force (SANDF): South African Army, South African Navy (SAN), South African Air Force (SAAF), Joint Operations Command, Military Intelligence, South African Military Health Services (2009) |
| South Georgia and the South Sandwich Islands | void |
| South Sudan | South Sudan Armed Forces |
| Southern Ocean | void |
| Spain | Spanish Armed Forces: Army (Ejercito de Tierra), Spanish Navy (Armada Espanola, AE; includes Marine Corps), Spanish Air Force (Ejercito del Aire Espanola, EdA) (2010) |
| Spratly Islands | void |
| Sri Lanka | Sri Lanka Army, Sri Lanka Navy, Sri Lanka Air Force (2010) |
| Sudan | Sudanese Armed Forces (SAF): Land Forces, Navy (includes Marines), Sudanese Air Force (Sikakh al-Jawwiya as-Sudaniya), Popular Defense Forces (2011) |
| Suriname | National Army (Nationaal Leger, NL; includes Marine Section and Air Wing) (2010) |
| Svalbard | no regular military forces |
| Swaziland | Umbutfo Swaziland Defense Force (USDF): Ground Force (includes Air Wing) (2010) |
| Sweden | Swedish Armed Forces (Forsvarsmakten): Army (Armen), Royal Swedish Navy (Marinen), Swedish Air Force (Svenska Flygvapnet) (2010) |
| Switzerland | Swiss Armed Forces: Land Forces, Swiss Air Force (Schweizer Luftwaffe) (2010) |
| Syria | Syrian Armed Forces: Syrian Arab Army, Syrian Arab Navy, Syrian Arab Air and Air Defense Forces (includes Air Defense Command) (2008) |