K3 may refer to:

Transportation

• China Railway K3/4
• K-3 (Kansas highway), a state highway in Kansas
• London Bus route K3
• Taquan Air, an Alaskan commuter airline (by IATA code)
• K-3 cart
• Kia Forte, a compact car sold as Kia K3 in South Korea
• Kia K3 (BL7), a subcompact car
• LNER Class K3, a class of British steam locomotives
• GSWRI Class K3, a Great Southern and Western Railway (Ireland) steam locomotive

Military

Units

• Life Regiment Hussars, Swedish cavalry regiment

Weapons

• K-3 (rifle), an Armenian-made bullpup rifle
• Daewoo K3, a light machine gun

Ships

• Soviet submarine K-3 Leninsky Komsomol, the first Soviet nuclear submarine
• USS K-3 (SS-34), a 1914 United States Navy K-class…Read more on Wikipedia