The Gulfstream II was announced by Grumman in 1965 as a turbofan-powered replacement for the Gulfstream I turboprop executive transport. The transformation could hardly have been more thorough: the G-II was equipped with an entirely new swept wing, and the pair of Rolls-Royce Spey turbofans were mounted on pylons just ahead of an all-new T-tail. For the operators of the 258 G-II models already in service, Gulfstream offered the Aircraft Service Change No. 300 retrofit: This package involved replacing the G-II wing with the new G-III wing, and included strengthening of the fuselage at the wing/fuselage junction, as well as an assortment of other modifications, such as replacement of the G-II’s steel brakes with carbon units and engine hush kits. The modified aircraft, designated the Gulfstream IIB, offers an increase in range of about 900 nm.

The landing gear is of the retractable tricycle type with dual wheels on each unit (the original G-II main gear is retained for installation on the new wing under the ASC 300 package.) The G-IIB features the wing of the G-III, complete with its drag-reducing Whitcomb winglets. The fuel system utilizes internal wing tanks only, and is essentially the same as the G-III fuel system, with the cockpit instrumentation modified accordingly.

The Gulfstream G-IIB has been completed in a variety of configurations, but typical executive cabins accommodate 10 to 14 passengers in combinations of club seating, side divan, and individual passenger seats. The aircraft is commonly outfitted with a large working galley, entertainment center, and full-sized aft lavatory. The standup cabins of the Gulfstream line have long been some of the largest available in corporate aircraft. The G-IIB cabin width is 7.3 ft., cabin height is 6.1ft. and length is 33.9ft.