Declassified British document give the yield of the W48 as 100 tonnes of TNT (0.42 TJ), making it one of the smallest nuclear weapons ever developed by the US.

[1] The history of the W48 began in April 1954 when the US Army expressed interest in a small low-yield nuclear projectile.

The initial development was the W33 8-inch (200 mm) gun-type projectile but the Army was interested in an improved or an even smaller diameter weapon.

[2] A study was commissioned to explore the development of a small-diameter implosion type artillery shell.

The technology at this time was not sufficiently advanced to develop such a weapon but significant progress was made by the University of California Radiation Laboratory (UCRL) over the next twelve months.

[2][3] Although the details of the study are classified, the results were positive enough that by September 1956 that emphasis moved to developing a 155 mm shell.

[3] In May 1957 Sandia stated that the 155 mm implosion-type projectile would require considerable development work and that the success of the program was not assured.

[3] As the Atomic Energy Commission was not equipped to study setback accelerations on shells, research into this matter was performed by the military.

[3] In January 1960 the Defense Atomic Support Agency wrote to Sandia indicating the weapon met the desired military characteristics with some exceptions.