Swan was a U.S. test nuclear explosive.
It was tested standalone as a test nuclear device on June 26, 1956 in shot Redwing Inca. It was tested again as the primary of a test thermonuclear device on July 2, 1956 in shot Redwing Mohawk. Both tests were successful in all respects. It subsequently served as the primary in numerous thermonuclear devices during the 1950s.
Most subsequent U.S. primaries are Swan-derived, including the Robin, the Tsetse, the Python and the much later (asymmetrical) ovoid (prolate) primaries.
The Swan device is the first design to incorporate a two-point hollow-pit air lens implosion assembly together with fusion boosting.
The Swan device had a yield of 15 kilotons, weighed 105 lb (47.6 kg), and had a (symmetrical) ovoid (non-prolate) shape with a diameter of 11.6 inches (29.5 cm) and a length of 22.8 inches (58 cm).
The above schematic illustrates what were probably its essential features.
A significant feature of these "two-point" implosion designs is "one-point safe". That is, accidental or intentional ignition of one of the two ignition "points" results in no nuclear yield as the "pit" is compressed into two separate parts, neither of which approaches critical mass.
The above schematics illustrate the essential features of this capability.
The super-precision turning machines (lathes) which constructed the components of Swan and Swan-derived primaries could accommodate workpieces which did not exceed 15.5 dia. x 54 inches (39.5 dia. x 137.2 cm); Swan and Swan-derived components were no larger than 12 dia. x 24 inches (30.5 dia. x 61.0 cm).