Swan was a United States test nuclear explosive, which was developed into the XW-45 warhead.
[http://nuclearweaponarchive.org/Usa/Tests/Redwing.html "Inca .. Yield: 15.2 kt. UCRL test of a multi-application boosted tactical nuclear warhead prototype named Swan. This design was later developed into the XW-45 warhead. The predicted yield was 10-15 kt."] The Swan device is the first design to incorporate a two-point ignition
hollow-pit air-
lens
A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements'') ...
implosion assembly together with
fusion boosting
A boosted fission weapon usually refers to a type of nuclear bomb that uses a small amount of Nuclear fusion, fusion fuel to increase the rate, and thus yield, of a Nuclear fission, fission reaction. The Fusion neutron, fast fusion neutrons rele ...
.
It was tested standalone on June 22, 1956, in shot
Redwing Inca.
It was tested again as the primary of a thermonuclear device on July 2, 1956, in shot
Redwing Mohawk.
[http://nuclearweaponarchive.org/Usa/Tests/Redwing.html "Mohawk. Yield: 360 kt This UCRL thermonuclear device used a boosted "Swan" primary and "Flute" secondary. The device was 15 inches in diameter, 46.2 inches long, and weighed 1116 lb. The primary was 11.6 inches by 22.8 inches and weighed 105 lb."] Both tests were successful.
Design features
The Swan device had a yield of 15 kilotons,
weighed , and had a (symmetrical) ovoid shape with a diameter of and a length of , a length to diameter ratio of 1.97.

The above schematic illustrates what were probably its essential features.
References
{{United States nuclear devices
Nuclear bombs of the United States