Aircraft

• O-1 Bird Dog, an observation aircraft manufactured by Cessna
• O-1 Falcon
  Curtiss Falcon
  The Curtiss Falcon is a family of military biplane aircraft built by the United States aircraft manufacturer Curtiss Aeroplane and Motor Company during the 1920s. Most saw service as part of the United States Army Air Corps as observation aircraft with the designations O-1 and O-11, or as the...
  
  , an observation aircraft manufactured by the Curtiss Aircraft Company
• O-1 Airship, an Italian manufactured semi-rigid airship operated by the US Navy

Military

• NATO Rank O-1
  Second Lieutenant
  Second lieutenant is a junior commissioned officer military rank in many armed forces.- United Kingdom and Commonwealth :The rank second lieutenant was introduced throughout the British Army in 1871 to replace the rank of ensign , although it had long been used in the Royal Artillery, Royal...
  
  
• USS O-1 (SS-62)
  USS O-1 (SS-62)
  USS O-1 was the lead ship of her class of submarine. Her keel was laid down on 26 March 1917 at the Portsmouth Navy Yard in Kittery, Maine. She was launched on 9 July 1918, and commissioned on 5 November 1918 with Lieutenant Commander Norman L...
  
  , lead ship of the United States O class submarines
• HNLMS O-1, a Royal Netherlands Navy O class submarine

Other

• O1 star, a subclass of O-class stars
  Stellar classification
  In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...
  
  
• O-1 tool steel, a type of oil-hardening tool steel
• O-1 visa
  O-1 Visa
  An O visa is a classification of non-immigrant temporary worker visa granted by the United States to aliens "who possesses extraordinary ability in the sciences, arts, education, business, or athletics, or who has a demonstrated record of extraordinary achievement in the motion picture or...
  
  
• Haplogroup O1 (Y-DNA)
  Haplogroup O1 (Y-DNA)
  In human genetics, Haplogroup O1 is a Y-chromosome DNA haplogroup. Haplogroup O1 is a descendent branch of the greater Haplogroup O.The great majority of Y-chromosomes within Haplogroup O1 belong to its subgroup O1a .-Origins:...
  
  , a Y-DNA haplogroup
• SP&S Class O-1, a steam locomotives class
• Otoyol 1
  Otoyol 1
  Otoyol 1 , abbreviated as , aka İstanbul 1. Çevreyolu , is a motorway in Istanbul, Turkey that forms the inner half ring road of the city connecting European and Asian parts via the Bosphorus Bridge....
  
  , a Turkish highway around Istanbul
• Ö1
  Ö1
  Ö1 is an Austrian radio station: one of the four national networks operated by Austria's public broadcaster ORF. It focuses on classical music, jazz, documentaries, features, news, radio plays, radio dramas, cabaret, quiz shows, and discussions.Ö1's programming mix of information, culture, music,...
  
  , an Austrian radio station
• O1 Communications, Inc., a California telecommunications company