Swan (nuclear primary)
Swan was a United States test nuclear explosive, which was developed into the XW-45 warhead. 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. Both tests were successful. Design features 
The Swan device is the first design to incorporate a two-point ignition hollow-pit air-lens implosion assembly together with fusion boosting. The Swan device had a yield of 15 kilotons, weighed , and had a (symmetrical) ovoid (non-prolate) 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 

Nuclear bombs of the United States