STRI - syst
- SWSS
- SWT
- SWTA
- SWTC
- SWTI
- SWTTEU
- SWW
- SWXO
- SWZ
- SX
- SXAD
- sxn
- sy
- SYADS
- SYDAS
- SYG
- sym
- sympathetic aerial detonation
- SYMWAR
- SYNADEX
- synchronized-time, automated reporting system
- synchronous altitude communications satellite
- synchronous communications (satellite)
- synchronous data acquisition system
- synchronous identification study
- synchronous identification system
- synchronous meteorological test satellite
- synchronous missile alarm system
- synchronous optical network
- synchronous satellite military communications system
- synchronous time-division multiplexing
- synchronous transmitter receiver
- SYNCOM
- synergistic defense suppression system
- synergistic innovation to gain military advantage
- SYNMAS
- SYNTAC
- SYNTEX
- synthetic air defense exercise
- synthetic aircraft turbine oil
