The Sukhoi Su-33 (Russian: Сухой Су-33) is an all-weather carrier-based air defence fighter designed by Sukhoi and manufactured by KnAAPO. It is a derivative of the Sukhoi Su-27 and was initially known as the Su-27K. First used in operations in 1995 aboard the carrier Tbilisi and Riga, the fighter officially entered service in August 1998, by which time the designation "Su-33" was used. Compared with the Su-27, the Su-33 has a strengthened undercarriage and structure, folding wings and stabilators, all for carrier operations. The wings are larger than on land-based aircraft for increased lift. The Su-33 has upgraded engines and a twin nose wheel, and is air refuellable.