RACER IV was a component of several of the first hydrogen bombs made by the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 during the 1950s. It was the first stage for three of the devices tested in four shots of the Castle series. They were shots Castle Bravo

Castle Bravo

Castle Bravo was the code name given to the first U.S. test of a dry fuel thermonuclear hydrogen bomb device, detonated on March 1, 1954 at Bikini Atoll, Marshall Islands, as the first test of Operation Castle. Castle Bravo was the most powerful nuclear device ever detonated by the United States ,...

 (Shrimp device), Romeo

Castle Romeo

Castle Romeo was the code name given to one of the tests in the Operation Castle series of American nuclear tests. It was the first test of the TX-17 thermonuclear weapon , the first deployed U.S...

 (Runt device), Union

Castle Union

Castle Union was the code name given to one of the tests in the Operation Castle series of American nuclear tests. It was the first test of the TX-14 thermonuclear weapon , one of the first deployed U.S...

 (Alarm Clock device) and Yankee

Castle Yankee

Castle Yankee was the code name given to one of the tests in the Operation Castle series of American tests of thermonuclear bombs.-Jughead:...

 (Runt II).

The Racer primary was developed in 1953 at Los Alamos

Los Alamos National Laboratory

Los Alamos National Laboratory is a United States Department of Energy national laboratory, managed and operated by Los Alamos National Security , located in Los Alamos, New Mexico...

 for the first generation of US thermonuclear weapons, the Mark 14

Mark 14 nuclear bomb

For the Sinclair Research Ltd. SC/MP based computer system see MK14.The Mark 14 nuclear bomb was a 1950s American thermonuclear bomb, the first solid-fuel staged hydrogen bomb. It was an experimental design, and only five units were produced in early 1954. It was tested in April 1954 during the...

, Mark 16

Mark 16 nuclear bomb

The Mark 16 nuclear bomb was a large thermonuclear bomb, based on the design of the Ivy Mike, the first hydrogen bomb test fired. The Mark 16 is more properly designated TX-16/EC-16 as it only existed in Experimental/Emergency Capability versions....

, and Mark 17

Mark 17 nuclear bomb

The Mark 17 and Mark 24 were the first mass-produced hydrogen bombs deployed by the United States. The two differed in their "primary" stages. The MK 17/24 bombs were long, diameter. They weighed 21 tons. The Mark 17 had a yield in the range of 25 megatons TNT equivalent...

 bombs. Racer was tested in the Upshot-Knothole

Operation Upshot-Knothole

Operation Upshot-Knothole was a series of eleven nuclear test shots conducted in 1953 at the Nevada Test Site.Over twenty-one thousand soldiers took part in the ground exercise Desert Rock V in conjunction with the Grable shot...

 series of tests with mock-up secondary stages as shots Nancy (Mark 14), Badger (Mark 16) and Simon (Mark 17)

Upshot-Knothole Simon

Upshot-Knothole Simon was a nuclear detonation conducted as part of the U.S. Operation Upshot-Knothole nuclear testing program. Simon was conducted on 25 April 1953 at the Nevada Test Site, and tested the TX-17/24 thermonuclear weapon design which had a yield of 43 kilotons....

. According to Chuck Hansen

Chuck Hansen

Chuck Hansen compiled, over a period of 30 years, the world's largest private collection of documents on how America developed the atomic bomb. These documents were obtained through the U.S...

, during the Upshot-Knothole tests the Racer had proven to have inconsistent yield, varying from 23 kilotons in the Badger shot to 43 kilotons in the Simon shot.

The design was revised and RACER IV was the version used as the primary in the stockpiled Mark 14 and Mark 17 bombs.