S55 may refer to:
Aircraft
- Savoia-Marchetti S.55, an Italian flying boat
- Sikorsky S-55, an American helicopter
- Sukhoi S-55, a proposed Russian fighter aircraft
Automobiles
- BMW S55, an automobile engine
- Mercedes-Benz S 55 AMG, a luxury car
- Mercury S-55, an American full-size car
- Shorland S55, a British armoured personnel carrier
Rail and transit
- S55 (New York City bus) serving Staten Island
- S55 (St. Gallen S-Bahn), a former S-Bahn line in Thurgau, Switzerland
- S55 (ZVV), a former line of the Zürich S-Bahn
- FGC line S55, a suburban train line in Catalonia, Spain
Other uses
- S55 (star) in the constellation Sagittarius
- Ariel 1, a British satellite
- County Route S55 (Bergen County, New Jersey)
- Explorer S-55 (satellite), a failed American spacecraft
- INS Sindhughosh (S55), a submarine of the Indian Navy
- Siemens S55, a mobile phone
- Wandandian language
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